DOE-based systems and devices for producing laser beams having modified beam characteristics

ABSTRACT

Novel methods are disclosed for designing and constructing miniature optical systems and devices employing light diffractive optical elements (DOEs) for modifying the size and shape of laser beams produced from a commercial-grade laser diodes, over an extended range hitherto unachievable using conventional techniques. The systems and devices of the present invention have uses in a wide range of applications, including laser scanning, optical-based information storage, medical and analytical instrumentation, and the like. In the illustrative embodiments, various techniques are disclosed for implementing the DOEs as holographic optical elements (HOEs), computer-generated holograms (CGHs), as well as other diffractive optical elements.

RELATED CASES

[0001] The present Application is a Continuation of application Ser. No.09/071,512 filed May 1, 1998, which relates to: application Ser. No.08/573,949 filed Dec. 18, 1995; application Ser. No. 08/726,522 filedOct. 7, 1995; application Ser. No. 08/886,806 filed Apr. 22, 1997,application Ser. No. 08/854,832 filed May 12, 1997; and application Ser.No. 08/949,915 filed Oct. 14, 1997; each said Application being commonlyowned by Metrologic Instruments, Inc. of Blackwood, N.J., andincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of Invention

[0003] The present invention relates generally to diffractive opticalelement (DOE) based optical systems of ultra-compact design capable ofmodifying the inherent elliptical, divergent, eccentric and astigmaticcharacteristics of laser beams produced from laser diode sources, suchas visible laser diodes (VLDs).

[0004] 2. Brief Description of the Prior Art

[0005] Laser diodes or visible laser diodes (VLD) are often used aslight sources in many scientific_and engineering applications. Whilelaser diodes offer significant advantages over other laser sources, e.g.gas lasers, in terms of efficiency, size, and cost, they neverthelesssuffer from several undesirable optical characteristics, namely: highbeam divergence, elliptical beam profile, and astigmatism. In order touse laser diodes in many communication, data-storage, scanning, andimaging applications, these inherent deficiencies in laser diodes mustbe corrected.

[0006] While complex refractive-optics type systems (employinganamorphic lenses and the like) have been developed for the purpose ofcorrecting for laser diode characteristics, such systems are generallybulky and expensive, and thus ill-suited for use in numerousapplications.

[0007] U.S. Pat. Nos. 5,247,162 and B1 4,816,660 disclose the use of alens and aperture-stop to shape the laser beam produced from a VLD foruse in laser scanners. While this technique provides an inexpensive wayof shaping the cross-section of a VLD laser beam, it does so at theexpense of a substantial loss in beam power. Moreover, this “pinhole”technique is incapable of correcting for astigmatism in laser beamsproduced by VLDs.

[0008] In recent years, alternative approaches to VLD beam shaping andcorrection have been developed. Such alternative techniques include, forexample, the use of: integrated-optics lenses; computer-generatedhologram (CGH) gratings; micro-Fresnel lenses; waveguide optics; andholographic optical elements (HOEs).

[0009] The use of HOEs for beam collimation, shaping/profiling andastigmatism-correction has received great attention, as such devices canbe made inexpensively and small in size to be used in CD-ROM players,consumer-products and analytical instruments employing VLDs and thelike. Examples of prior art laser diode beam-correction techniquesemploying HOEs are disclosed in the following journal articles:“Efficient Beam-Correcting Holographic Collimator For Laser Diodes” byA. Aharoni, et al., published in Vol. 17, No. 18, OPTICS LETTERS, Sep.15, 1992, at pages 1310-1312; “Beam-Correcting Holographic Doublet ForFocusing Multimode Laser Diodes” by A. Aharoni, et al., published inVol.18, No.3, OPTICS LETTERS, Feb. 1, 1993, at pages 179-181; and“Design of An Optical Pickup Using Double Holographic Lenses” byHiroyasu Yoshikawa, et al., published in SPIE, Vol. 2652, 1996, at pages334-340.

[0010] While the above-cited prior art publications disclose dual-HOEoptics systems for beam-collimation, beam-shaping and astigmatismcorrection, such prior art design methods do not enable the design andconstruction of laser beams having any degree of astigmatism,focal-distance, spot-size, focused-spot aspect-ratio, and zerodispersion. These are critical requirements in many laser scanning barcode reading applications.

[0011] Prior art HOE-based systems do not address the fact thatcommercial VLDs suffer from beam eccentricity (i.e. poor beam pointingcharacteristics). Consequently, it has not been possible to successfullycarry out many design objectives by virtue of the fact that assumptionsmade during system design are not satisfied during design realization.

[0012] Accordingly, there is a great need in the art for an improvedmethod of designing and constructing optical systems for modifying theelliptical, divergent, eccentric and astigmatic characteristics of laserbeams inherently produced from commercial-grade laser diodes, whileavoiding the shortcomings and drawbacks of prior art systems, devices,and methodologies.

OBJECTS AND SUMMARY OF THE PRESENT INVENTION

[0013] Thus, it is a primary object of the present invention to providean improved method of designing optical systems for modifying theinherent elliptical, divergent, eccentric and characteristics of a laserdiodes, while avoiding the shortcomings and drawbacks of prior artsystems, devices, and methodologies.

[0014] Another object of the present invention is to provide a novellaser beam modification system employing a plurality of diffractiveoptical elements (DOES) for modifying the size and shape of a laser beamproduced from a commercial-grade laser diode, such as a VLD, over anextended range which has hitherto been impossible to achieve usingconventional techniques, while avoiding the introduction of dispersionin the output laser beam which is commonly associated with prior art HOEdoublets and the like.

[0015] Another object of the present invention is to provide such aDOE-based laser beam modifying system, wherein the inherent astigmatismcharacteristics associated with a VLD are eliminated or minimized.

[0016] Another object of the present invention is to provide a DOE-basedlaser beam modifying system, wherein beam dispersion is minimized, ornormal dispersion or reverse dispersion characteristics are provided forany given beam compression or expansion ratio, by selecting the properangle between the two DOEs of the system.

[0017] Another object of the present invention is to provide a DOE-basedlaser beam modifying system, wherein beam dispersion is minimized forthe system acting alone, or fine-tuned to compensate for the dispersionof other elements preceding it or following the system.

[0018] Another object of the present invention is to provide a laserbeam modifying system capable of producing a laser beam having a desiredspot-size over a specified depth of field, achieved by focusing thelaser beam with a lens (or variable DOE of a selected type), and thenreshaping the laser beam using a pair of DOEs.

[0019] Another object of the present invention is to provide a laserbeam producing system employing a set of beam-modifying DOEs whichproduce zero dispersion while simultaneously providing any desiredaspect-ratio for the beam leaving (exiting) the second DOE.

[0020] Another object of the present invention it to provide a HOE-basedlaser beam modifying system adapted for use in a broad range ofapplications employing VLDs, which includes, but is not limited to,laser scanning applications.

[0021] Another object of the present invention it to provide a CGH-basedlaser beam modifying system adapted for use in a broad range ofapplications employing VLDs, which includes, but is not limited to,laser scanning applications.

[0022] Another object of the present invention is to provide anultra-compact DOE-based device capable of collimating or focusing laserbeams produced from astigmatic VLDs while minimizing dispersion beamdispersion and correcting for beam ellipticity.

[0023] A further object of the present invention is to provide anultra-compact optics module for modifying the aspect-ratio of laserbeams produced by VLDs, while eliminating beam astigmatism introduced byvirtue of the inherent astigmatic difference in the VLD, and minimizingdispersion in the output laser beam created by wavelength-dependentvariations in the spectral output of the VLD, such as superluminescence,multi-mode lasing, and laser mode hopping.

[0024] Another object of the present invention is to provide a noveloptical-bench module which enables easy mounting and alignment ofselected components of the laser beam producing systems of the presentinvention so that the inherently elliptical beam produced fromcommercial VLDs is simply aligned on the optical axis of the system.

[0025] Another object of the present invention is to provide a novelDOE-based laser beam producing device, wherein refractive optics (L1)having an axially symmetric surface profile characteristics are disposedbetween the laser diode source (VLD) and the diffractive optics (e.g.DOEs D1 and D2), to enable the use the DOEs to modify (e.g. correct oreliminate) astigmatism in the output laser beam, while simplifying themanufacture of the refractive optics (L1) and diffractive optics (DOEsD1 and D2), reducing the cost of optical elements, and simplifyingparameter alignment during the assembly process.

[0026] Another object of the present invention is to provide a noveloptics module employing a pair of DOEs configured in the beamcompression mode, wherein the total expansion factor (M) of the DOEcombination is less than one, so that the size of the laser beam in theplane of diffraction is compressed without changing the beam size in thedimension perpendicular to the plane of diffraction.

[0027] Another object of the present invention is to provide a noveloptics module employing a pair of DOEs configured in the beam expansionmode, wherein the total expansion factor (M) of the DOE combination isgreater than one, so that the size of the laser beam in the plane ofdiffraction is expanded without changing the beam size in the dimensionperpendicular to the plane of diffraction.

[0028] A further object of the present invention is to provide a novellight diffractive optics module for incorporation into small laserscanning devices, such as laser scan-engines, as well as replacingconventional prisms and anamorphic lenses used in VLD-based opticalsystems such as optical storage devices, CD-ROM players and recorders,and like systems and devices.

[0029] Another object of the present invention is to provide a DOE-basedoptics module for modifying the aspect-ratio of a VLD beam whilesimultaneously controlling beam dispersion to minimize the overalldispersion of the optical system in which it is being used.

[0030] Another object of the present invention is to provide such anoptics module, wherein beam astigmatism inherently associated with VLDsis eliminated or minimized.

[0031] Another object of the present invention is to provide a novelmethod for designing a dual-HOE laser beam modifying system, in which apair of equations are solved under a given set of conditions whichensures that beam dispersion is eliminated and a desired expansionfactor (M) is obtained.

[0032] Another object of the present invention is to provide such anoptical design method, wherein analytical and spreadsheet-type programsare combined in an integrated fashion to allow for easy design andanalysis of the optics module under consideration.

[0033] Another object of the present invention is to provide a dual-DOEoptics module particularly designed for replacing “pinhole” type beamshaping modules used in laser scanning bar code symbol readers.

[0034] Another object of the present invention is to provide a novelsystem for precisely and rapidly aligning the parameters of the opticsmodules of the present invention to enable the inexpensive massproduction of such optical systems and devices for widespread use indiverse fields of endeavor.

[0035] Another object of the present invention is to provide such aparameter alignment system, wherein micro-adjustment of the opticalcomponents of the laser beam producing modules of the present inventionare carried out in a fully automated manner under microcomputer control,thereby allowing (i.e. enabling) mass-production of DOE-based laser beamproducing modules which satisfy high quality-control (QC) measures.

[0036] Another object of the present invention is to provide a novelmethod of designing an ultra-compact HOE-based device for producing alaser beam having a selected set of beam characteristics obtained bymodifying the astigmatic, elliptical light beams produced frominexpensive VLDs.

[0037] Another object of the present invention is to provide a hand-heldlaser scanner, wherein the laser beam producing system of the presentinvention is embodied to enable the production of laser beams for barcode scanning operations.

[0038] Another object of the present invention is to provide abody-wearable laser scanner, wherein the laser beam producing system ofthe present invention is embodied to enable the production of laserbeams for bar code scanning operations.

[0039] Another object of the present invention is to provide a laserscanning-engine, wherein the laser beam producing system of the presentinvention is embodied to enable the production of laser beams for barcode scanning operations.

[0040] Another object of the present invention is to provide in-counterscanners, projection scanners, pass-through (passive) scanners, laserpointers, and the like, wherein the laser beam producing system of thepresent invention is embodied.

[0041] Another object of the present invention is to provide aholographic laser scanner, wherein one or more laser beam producingmodules of the present invention are embodied to enable the productionof a plurality of laser beams for bar code scanning operations.

[0042] Another object of the present invention is to provide a CD-ROMplaying unit, wherein the laser beam producing system of the presentinvention is embodied to enable the production of laser beams forreading information digitally recorded within a CD-ROM or like recordingdevice.

[0043] Another object of the present invention is to provide alaser-based instrument, wherein the laser beam producing system of thepresent invention is embodied to enable the production of laser beamsfor diagnosis or detection of various conditions.

[0044] These and other objects of the present invention will becomeapparent hereinafter and in the claims to Invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more fully understand the Objects of the PresentInvention, the following Detailed Description of the IllustrativeEmbodiments should be read in conjunction with the accompanying FigureDrawings, wherein:

[0046]FIG. 1 is a schematic representation of a general model for theDOE-based laser beam producing system of the present invention, showingits laser source and the DOE-based laser beam modifying subsystem;

[0047]FIG. 1A is a schematic representation of the dual-DOE opticalsubsystem used in the various illustrative embodiments of the laser beamproducing system of the present invention, identifying the geometricaloptical parameters employed in the design of this subsystem;

[0048]FIG. 2A is a geometrical optics model of the first illustrativeembodiment of the DOE-based laser beam producing subsystem according tothe principles of the present invention;

[0049]FIG. 2B is a geometrical optics model of the second illustrativeembodiment of the DOE-based laser beam producing subsystem according tothe principles of the present invention;

[0050]FIG. 2C is a geometrical optics model of the third illustrativeembodiment of the DOE-based laser beam producing subsystem according tothe principles of the present invention;

[0051]FIG. 2D is a geometrical optics model of the fourth illustrativeembodiment of the DOE-based laser beam producing subsystem according tothe principles of the present invention;

[0052]FIG. 2E is a geometrical optics model of the fifth illustrativeembodiment of the DOE-based laser beam producing subsystem according tothe principles of the present invention;

[0053]FIG. 2F is a geometrical optics model of the sixth illustrativeembodiment of the DOE-based laser beam producing subsystem according tothe principles of the present invention;

[0054]FIG. 2G is a geometrical optics model of the seventh illustrativeembodiment of the DOE-based laser beam producing subsystem according tothe principles of the present invention;

[0055]FIG. 2H is a geometrical optics model of the eighth illustrativeembodiment of the DOE-based laser beam producing subsystem according tothe principles of the present invention;

[0056]FIG. 21 is a geometrical optics model of the ninth illustrativeembodiment of the DOE-based laser beam producing subsystem according tothe principles of the present invention;

[0057]FIG. 2J is a geometrical optics model of the tenth illustrativeembodiment of the DOE-based laser beam producing subsystem according tothe principles of the present invention;

[0058]FIG. 2K is a geometrical optics model of the eleventh illustrativeembodiment of the DOE-based laser beam producing subsystem according tothe principles of the present invention;

[0059]FIG. 2L is a geometrical optics model of the twelfth illustrativeembodiment of the DOE-based laser beam producing subsystem according tothe principles of the present invention;

[0060]FIG. 2M is a geometrical optics model of the thirteenthillustrative embodiment of the DOE-based laser beam producing subsystemaccording to the principles of the present invention;

[0061]FIG. 2N is a geometrical optics model of the fourteenthillustrative embodiment of the DOE-based laser beam producing subsystemaccording to the principles of the present invention;

[0062] FIGS. 3A1 through 3A3 set forth a flow chart illustrating thesteps involved in carrying out the method of designing DOE-based laserbeam producing systems according to the present invention, whereinastigmatism can be tolerated and adjustment of the focal-length of theresulting stigmatic beam is not required;

[0063] FIGS. 3B1 through 3B3 set forth a flow chart illustrating thesteps involved in carrying out the method of designing DOE-based laserbeam producing systems, wherein astigmatism correction is desired andadjustment of the focal-length of the resulting stigmatic beam is notrequired;

[0064] FIGS. 3C1 through 3C3 set forth a flow chart illustrating thesteps involved in carrying out the method of designing DOE-based laserbeam producing systems, wherein astigmatism correction and adjustment ofthe focal-length of the resulting stigmatic beam are required;

[0065] FIGS. 3D1 through 3D3, taken together show a flow chart, setforth a flow chart illustrating the steps involved in carrying out themethod of designing DOE-based laser beam producing systems, whereinastigmatism correction is desired and adjustment of the focal-length ofthe resulting stigmatic beam and delta-focusing are not required;

[0066]FIG. 3E is a “central-ray” type geometrical optics model of theDOE-based laser beam modifying subsystem employed within each of theillustrative embodiments of the laser beam producing systems of thepresent invention;

[0067] FIGS. 3F1 through 3F2 set forth a flow chart illustrating thesteps involved in carrying out the method of designing the DOE-basedlaser beam modifying subsystem of the present invention so thatpre-selected design criteria is satisfied;

[0068]FIG. 4A sets forth a flow chart illustrating a preferred method ofconverting the design parameters of a HOE into its constructionparameters expressed at the construction wavelength;

[0069]FIG. 4B is a schematic diagram showing apparatus for recordingHOEs to be used in the dual-HOE subsystem specified in FIG. 4A;

[0070] FIGS. 4C1 and 4C2 collectively set forth a flow chartillustrating the basic steps involved in constructing a CGHimplementation of the DOE-based laser beam modifying subsystem hereof;

[0071]FIG. 4D is a schematic diagram showing apparatus for generatingand recording master CGHs, and producing copies thereof for use inDOE-based subsystems in accordance with the principles of the presentinvention;

[0072]FIG. 5A is a schematic diagram of an optical arrangement foranalyzing dispersion in the laser beam output from the DOE-based laserbeam modifying subsystem of the present invention;

[0073]FIG. 5B is a generalized graphical representation of two differentdispersion characteristics of a laser beam producing system of thepresent invention when operated in different modes of operation, shownplotted as a function of output wavelength;

[0074]FIG. 5B1 is a graphical representation of the dispersioncharacteristics of an exemplary laser beam producing system of the typeshown in FIGS. 2A and 7A-7C, showing a negative (concave down) curvaturewhen plotted as a function of output wavelength;

[0075]FIG. 5B2 is a graphical representation of the dispersioncharacteristics of a laser beam producing system of the type shown inFIGS. 2A and 7A-7C if the direction of propagation of the laser beam isreversed, thereby exhibiting a positive (concave upward) curvature,plotted as a function of output wavelength;

[0076]FIG. 6A is a first perspective view of a first illustrativeembodiment of a laser beam producing module according to the presentinvention, wherein its VLD laser source is adjustable relative to itsimaging lens (L1) and pair of stationary-mounted HOEs and beam directingmirror so that the elliptical beam produced from the VLD is alignedrelative to the optical axes of the HOEs in order to minimize laser beamdispersion and to control the aspect-ratio of the output laser beam in adesired manner;

[0077]FIG. 6B is a second perspective view of the laser beam producingmodule shown in FIG. 6A;

[0078]FIG. 6C is a plan view of the laser beam producing module shown inFIG. 6A;

[0079]FIG. 7A is a perspective view of a second illustrative embodimentof the laser beam producing module of the present invention, wherein itsVLD laser source is adjustable relative to its imaging lens (L1) andpair of stationary-mounted HOEs so that the inherently off-axiselliptical beam produced from the VLD is aligned relative to the opticalaxes of the HOEs in order to minimize beam dispersion and control theaspect ratio of the output laser beam in a desired manner;

[0080]FIG. 7B is an exploded view of the laser beam producing module ofthe present invention shown in FIG. 7A, showing its heat-sink plate,VLD, VLD-yoke, lens L1, HOES H1 and H2, optics module base, and coverplate;

[0081]FIG. 7C is a plan view of the laser beam producing module shown inFIG. 7A;

[0082]FIG. 8A is a perspective view of a miniature laser scanning modulefor use in connection with laser beam producing modules of the presentinvention;

[0083]FIG. 8B is an exploded view of the laser beam scanning module ofthe present invention shown in FIG. 8A, showing its scanning element,mounting plates, electromagnet, support base, and cover plate;

[0084]FIG. 9 is a plan view of the laser beam producing module of thepresent invention shown in FIG. 7A configured for cooperation with thelaser beam scanning module shown in FIG. 8A;

[0085]FIG. 10A is perspective view of the third illustrative embodimentof the laser beam producing module of the present invention, wherein alaser beam scanning mechanism is integrated therein and its VLD lasersource is adjustable relative to its imaging lens (L1) and pair ofstationary-mounted HOEs so that the inherently off-axis elliptical beamproduced from the VLD is aligned relative to the optical axes of theHOEs in order to minimize laser beam dispersion, and control theaspect-ratio of the output laser beam in a desired manner;

[0086]FIG. 10B is an exploded view of the laser beam producing moduleshown in FIG. 10A, showing its heat-sink plate, VLD, VLD-yoke, lens L1,HOES H1 and H2, optics module base, scanning element, mounting plates,electromagnet, and cover plate;

[0087]FIG. 10C is a cross-section view of the laser beam producingmodule taken along line 10C-10C;

[0088]FIG. 10D is an exploded perspective view of the laser beamproducing module of FIG. 10A mounted within a miniature housing of alaser beam scanning engine;

[0089]FIG. 11A is a perspective view of a fourth illustrative embodimentof the laser beam producing module of the present invention, wherein itsVLD laser source is adjustable relative to its imaging lens (L1) and sothat the inherently off-axis elliptical beam produced from the VLD isaligned relative to the optical axes of the HOEs in order to minimizelaser beam dispersion, control the aspect-ratio of the output laser beamin a desired manner, and correct for astigmatism in the output laserbeam, the focal length of the second lens (L2) is adjustable tofine-tune the focal-length of the output laser beam as required by theapplication to which the laser beam producing system is put;

[0090]FIG. 11B is an exploded view of the laser beam producing moduleshown in FIG. 11A, showing its sub-components and mechanisms enablingthe adjustment of the position of the VLD relative to the lens L1 andthe position of HOE H2 relative to HOE H1;

[0091]FIG. 11C is a cross-section view of the laser beam producingmodule taken along line 11C-11C shown in FIG. 11A;

[0092]FIG. 12A is a perspective view of the fifth illustrativeembodiment of the laser beam producing module of the present invention,wherein a laser beam scanning mechanism is integrated therein and itsVLD laser source is adjustable relative to its imaging lens (L1) so thatthe inherently off-axis elliptical beam produced from the VLD is alignedrelative to the optical axes of the HOEs in order to minimize laser beamdispersion, and control the aspect-ratio of the output laser beam in adesired manner, correction for astigmatism in the output laser beam;

[0093]FIG. 12B is an exploded view of the laser beam producing moduleshown in FIG. 12A showing its subcomponents and mechanisms enabling theadjustment of the position of the VLD relative to the lens L1, theposition of HOE H2 relative to HOE H1, and the focal length of lens L2which can be realized as a compound lens system;

[0094]FIG. 12C is a cross-section view of the laser beam producingmodule taken along line 12C-12C shown in FIG. 12A;

[0095]FIG. 13 is a schematic representation of a parameter adjustmentsystem for aligning the optical components within the various types oflaser beam producing modules of the present invention disclosed herein;

[0096]FIG. 14 is a schematic diagram of the laser beam producing moduleof FIG. 7A installed upon the parameter adjustment system of FIG. 13,for aligning optical components in the module so that laser beamdispersion is minimized and the aspect-ratio of the output laser beam iscontrolled in a desired manner;

[0097]FIG. 15 is a schematic diagram of the laser beam producing moduleshown in FIG. 11A installed upon the parameter adjustment system of FIG.13, for aligning optical components of the module so that laser beamdispersion is minimized, the aspect-ratio of the output laser beam iscontrolled in a desired manner, and astigmatism in the output laser beamis corrected, e.g. eliminated;

[0098]FIG. 16 is a schematic diagram of the laser beam producing moduleshown in FIG. 12A installed upon the parameter adjustment system of FIG.13, for aligning the optical components of the module so that laser beamdispersion is minimized, the aspect-ratio of the output laser beam iscontrolled in a desired manner, astigmatism in the output laser beam iscorrected, and adjustment of the focal-length of the resulting stigmaticbeam is achieved;

[0099]FIG. 17 is a schematic diagram of the laser beam producing moduleshown in FIG. 12A installed upon the parameter adjustment system of FIG.13, for aligning the optical components of the module so that laser beamdispersion is minimized, and astigmatism in the output laser beam iscorrected, without focus control or focal length adjustment;

[0100]FIG. 18 is a schematic representation of a hand-supportable laserscanning system constructed in accordance with the present invention,wherein one or more DOE-based laser beam producing systems of thepresent invention are configured and driven by a synchronized drivercircuit for producing a 2-D laser scanning pattern suitable foromni-directional or raster scanning of bar code symbols;

[0101]FIG. 19 is a schematic representation of a fixed-type projectionlaser scanning system, wherein a laser beam producing subsystem of thepresent invention is used to produce a laser beam having desired beamcharacteristics for omni-directional laser scanning;

[0102]FIG. 20 is a schematic representation of a body-wearable laserscanning system which embodies an DOE-based laser beam producing moduleof the present invention within its finger-mounted scanning module;

[0103]FIG. 21 is a schematic representation of a holographic laser beamscanning system, wherewith a plurality of laser beam producing modulesof the present invention cooperate with a holographic laser scanningdisc and a plurality of wavelength-compensation gratings to produce anomni-directional scanning pattern within a 3-D scanning volume;

[0104]FIG. 22 is a schematic representation of a CD-ROM player in whicha laser beam producing module according to the present invention isintegrated;

[0105]FIG. 23 is a schematic representation of a laser beam pointingdevice, wherein a laser beam producing module according to the presentinvention is embodied; and

[0106]FIG. 24 is a schematic representation of an analytical instrument,in which a laser beam producing module according to the presentinvention is employed for detection or diagnosis of a particularcondition.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS OF THE PRESENTINVENTION

[0107] In accordance with one broad aspect of the present invention,illustrated in FIG. 1, novel apparatus 1 employs a light-diffractiveoptical subsystem 2 for modifying the inherent beam characteristics of alaser beam 3 generated from a laser diode source 4 (e.g. visible laserdiode or VLD). Preferably, the laser diode source 4 has the so-calledheterostructure or double-heterostructure, or multi-quantum wellconstruction. The laser beam output from the laser diode source 4 ismodified by optical subsystem 2, and the modified beam characteristicsassociated therewith, are suited by design for use in particularapplications. Hereinafter, apparatus according to this first aspect ofthe present invention, adapted for modifying the characteristics oflaser beams produced from laser diode sources, shall be referred to as“a laser beam modifying subsystem”.

[0108] Each embodiment of the laser beam-modifying system of the presentinvention is designed using the beam characteristics of the particularlaser source 4 employed in the system. As shown in FIG. 1A, the opticalsubsystem 2 comprises: a lens element (L1); and at least two lightdiffractive optical elements (DOEs), indicated by D1 and D2,respectively, in FIG. 1A. The primary function of optical subsystem 2 isto modify the laser beam produced from the laser diode source 4 so thatthe resulting laser beam 5 output from DOEs D1 and D2 has predetermined(modified) beam characteristics that are suited by design for use inparticular applications. Hereinafter, apparatus according to this secondaspect of the present invention, adapted for producing laser beamshaving predetermined beam characteristics, shall be referred to as“laser beam producing system”.

[0109] In defining the laser beam modifying (optics) subsystem 2, theangle of incidence of the laser beam from the lens D1 onto the frontsurface of the first diffractive optical element (DOE) D1 is specifiedby θ_(i1) whereas the angle of diffraction therefrom is specified byθ_(d1). The angle of incidence of the laser beam from the first DOE D1onto the front surface of second fixed DOE D2 is specified by θ_(i2),whereas the angle of diffraction therefrom is specified by θ_(d2). Theangle ρ between the surfaces of the two DOEs D1 and D2 as:

ρ=θ_(d1)−θ_(i2)

[0110] These five parameters θ_(i1), θ_(d1), θ_(i2), θ_(d2), and ρcompletely define the dual-DOE subsystem, and thus provide four degreesof freedom within the geometrical optics model thereof.

[0111] Hereinbelow, a number of illustrative embodiments of the laserbeam producing system according to the present invention will now bedescribed in great detail. In such illustrative embodiments shown in thefigures of the accompanying Drawings, like structures and elements shallbe indicated by like reference numerals.

[0112] Description of Illustrative System Embodiments Of The LaserBeam-Producing System Of The Present Invention

[0113] In each of the fourteen illustrative embodiments described below,the laser beam is produced from a VLD 4 having the so-calledheterostructure or double-heterostructure, or multi-quantum wellconstruction. In a typical VLD, the beam divergence will be less in thedirection parallel to the VLD junction. Also, in all commerciallyproduced VLDs, the electric field (E-field) of the laser beam isoriented (i.e polarized) in a direction parallel to the narrowdivergence direction of the beam, which is generally parallel to thejunction of the VLD.

[0114] In order to understand the operation of commercial VLDs whichinherently produce astigmatic beams, it will be helpful to construct amodel thereof, as done in copending application Ser. No. 08/573,949filed Dec. 18, 1995, incorporated herein by reference. According to thismodel, the laser beam exiting the diode source is deemed to be generatedfrom a combination of sources, namely: a S “source” and a P “source”coaxially located inside the VLD, but separated by a distance referredto as the astigmatic difference or simply the astigmatism of the VLD.Each wave source in this model creates an independent cylindricalwavefront which interacts with the other wave source to create an effecton the resulting wavefront that results in the astigmatism. In the casewhere the astigmatism is zero, the two cylindrical sources coincide andthe resultant wavefront is spherical. The P source is considered thesource of origin of the narrow divergence portion of the beam (and thusP shall hereinafter refer to the direction parallel to the VLDjunction). The S source is considered the source of origin of the widedirection of the beam (and thus S—derived from the German word“Senkrecht” meaning “perpendicular”—shall hereinafter refer to thedirection perpendicular to the VLD junction).

[0115] Ideally, to ensure the highest diffraction efficiency of thelaser beam transmitted through the DOEs D1 and D2, the diffracted laserbeam at angle θ_(d1) should be in the “plane of incidence” of theincoming beam at DOE D1. In accordance with standard definitions, the“plane of incidence” shall mean the plane containing the incident lightray at DOE D1 and the normal to the surface of DOE D1 at the point ofincidence thereon. It is not possible to define a plane of incidence fora cone of rays incident the surface of lens L1. Also, the diffractedlaser beam at angle θ_(d2) relative to DOE D2 should be in the “plane ofincidence” of the incident beam at DOE D2, and the plane of incidence atDOE D1 should be coplanar with the plane of incidence at DOE D1 (i.e.disposed within a common plane), to ensure the highest possible lightdiffraction efficiency as the laser beam passes through the dual-DOEbeam modifying subsystem 6. Regardless of how the DOEs are implemented(e.g. as HOEs, CGHs, surface-relief holograms, etc), the fringestructure of the DOEs must be arranged perpendicular to the (common)plane of incidence at the DOEs in order to achieve maximum lightdiffraction efficiency through this subsystem. With this generalarrangement, it is noted that all modifications to the laser beamexiting the VLD (e.g. compression or expansion) will occur within the“common plane of incidence” passing through DOEs D1 and D2.

[0116] Depending on the application at hand, there may be a need tocompress or expand a particular dimension of the astigmatic laser beamexiting from the VLD. In order to perform such beam modifying functionsupon this laser beam, the individual expansion ratios for DOEs D1 andD2, designated by M₁ and M₂, respectively, will be selected by theoptical system designer so that the beam-shaping factor (e.g. expansionratio) of the DOE-subsystem, M=M₁M₂, is greater than unity when beamexpansion is required, and less than unity when beam compression isrequired. In the DOE subsystem, the individual expansion ratios aregiven by the following formulas: M₁=D_(output1)/D_(input1) andM2=D_(output2)/D_(input2), wherein D represents dimension of the beam inthe compression/expansion direction (i.e. common plane of incidence ofDOEs D1 and D2).

[0117] There are four general cases of laser beam modification that maybe carried out by any particular embodiment of the laser beam producingsystem of the present invention. These cases will now be brieflydescribed below to provide an overview of the system of the presentinvention.

[0118] In the first general case of beam modification, the widerdimension of the laser beam requires compression by the DOE-basedsubsystem. In this case, the DOEs D1 and D2 are designed so that thebeam-shaping factor M thereof is less than unity and the narrowerdimension of the laser beam exiting the VLD is oriented perpendicular tothe “common” plane of incidence passing through DOEs D1 and D2. As thislatter condition is satisfied by orienting the VLD junction (and thusits narrower beam dimension and polarization direction) perpendicular tothe common plane of incidence, the laser beam incident on DOE D1 is saidto be “S-polarized” or “S-incident” on the surface of DOE D1, that isthe E-field of the incident laser beam is perpendicular to the commonplane of incidence. In this configuration, the wider dimension of thelaser beam is disposed within the common plane of incidence (whereindiffraction occurs) so that beam compression results as desired by thedesign, while the narrower beam dimension is disposed perpendicularthereto (wherein no diffraction occurs) so that no beam compressionresults along this dimension as desired by the design. In this case, anelliptical laser beam can be made less elliptical or circular.

[0119] In the second general case of beam modification, the narrowerdimension of the laser beam requires compression by the DOE-basedsubsystem. In this case, the DOEs D1 and D2 are designed so that thebeam-shaping factor M thereof is less than unity and the narrowerdimension of the laser beam exiting the VLD is oriented parallel to the“common” plane of incidence passing through DOEs D1 and D2. As thislatter condition is satisfied by orienting the VLD junction (and thusits narrower beam dimension and polarization direction) parallel to thecommon plane of incidence, the laser beam incident on DOE D1 is said tobe “P-polarized” or “P-incident” on the surface of DOE D1, that is theE-field of the incident laser beam is parallel to the common plane ofincidence. In this configuration, the narrower dimension of the laserbeam is disposed within the common plane of incidence (whereindiffraction occurs) so that beam compression results as desired by thedesign, while the wider beam dimension is disposed perpendicular thereto(wherein no diffraction occurs) so that no beam compression resultsalong this dimension as desired by the design. In this case, anelliptical laser beam can be made more elliptical.

[0120] In the third general case of beam modification, the widerdimension of the laser beam requires expansion by the DOE-basedsubsystem. In this case, the DOEs D1 and D2 are designed so that thebeam-shaping factor M thereof is greater than unity and the narrowerdimension of the laser beam exiting the VLD is oriented perpendicular tothe “common” plane of incidence passing through DOEs D1 and D2. As thislatter condition is satisfied by orienting the VLD junction (and thusits narrower beam dimension and polarization direction) perpendicular tothe common plane of incidence, the laser beam incident on DOE D1 is saidto be “S-polarized” or “S-incident” on the surface of DOE D1, that isthe E-field of the incident laser beam is perpendicular to the commonplane of incidence. In this configuration, the wider dimension of thelaser beam is disposed within the common plane of incidence (whereindiffraction occurs) so that beam expansion results as desired by thedesign, while the narrower beam dimension is disposed perpendicularthereto (wherein no diffraction occurs) so that no beam expansionresults along this dimension as desired by the design. In this case, anelliptical laser beam can be made more elliptical.

[0121] In the fourth general case of beam modification, the narrowerdimension of the laser beam requires expansion by the DOE-basedsubsystem. In this case, the DOEs D1 and D2 are designed so that thebeam-shaping factor M thereof is greater than unity and the narrowerdimension of the laser beam exiting the VLD is oriented parallel to the“common” plane of incidence passing through DOEs D1 and D2. As thislatter condition is satisfied by orienting the VLD junction (and thusits narrower beam dimension and polarization direction) parallel to thecommon plane of incidence, the laser beam incident on DOE D1 is said tobe “P-polarized” or “P-incident” on the surface of DOE D1, that is theE-field of the incident laser beam is parallel to the common plane ofincidence. In this configuration, the narrower dimension of the laserbeam is disposed within the common plane of incidence (whereindiffraction occurs) so that beam expansion results as desired by thedesign, while the wider beam dimension is disposed perpendicular thereto(wherein no diffraction occurs) so that no beam expansion results alongthis dimension as desired by the design. In this case, an ellipticallaser beam can be made less elliptical or circular.

[0122] Using the above-described principles, numerous embodiments of thelaser beam producing system of the present invention can be designed andconstructed using various types of enabling technologies. Below,fourteen different illustrative embodiments of the laser beam producingsystem hereof shall be described in detail. In each of theseillustrative embodiments of the present invention, the angles ofincidence and diffraction at the DOEs are the only parameters thatdetermine whether the incident laser beam is compressed or expanded. Fora fixed set of DOE angles, the polarization direction of the laser beamwill determine whether the aspect ratio of the elliptical beam isincreased or decreased. This is due to the direct relationship thatexists between the narrow dimension and the polarization direction ofthe laser beam exiting a VLD.

[0123] In each of the beam compression embodiments, an S-polarized beamas well as a P-polarized beam incident DOE D1 will be compressed. Thedifference between such cases is that the elliptical S-polarized beamwill become less elliptical while the P-polarized beam will become moreelliptical. In many instances where beam compression is desired orrequired, an S-polarized beam will be preferred as its beam aspect ratiowill be reduced while its beam cross-section is made smaller.

[0124] In each of the beam expansion embodiments, an S-polarized beam aswell as a P-polarized beam incident DOE D1 will be expanded. Thedifference between such cases is that the elliptical S-polarized beamwill become more elliptical while the P-polarized beam will become lesselliptical. In many instances where beam expansion is desired orrequired, a P-polarized beam will be preferred as its beam aspect ratiowill be reduced while its beam cross-section is made larger.

[0125] First Illustrative System Embodiment Of The Laser Beam ProducingSystem Of The Present Invention

[0126] In FIG. 2A, the first illustrative embodiment of the laser beamproducing system hereof (“System Embodiment No. 1”) comprises: a laserbeam source, such as a visible laser diode (VLD), (e.g. Sony ModelSLD1122VS) for producing a laser beam from its junction typically havingdivergent and elliptical beam characteristics; a collimating lens (L1),realizable as a refractive lens e.g. a {fraction (4/35)} mm lens, a HOE,other type of DOE, a grin lens, one or more zone plate(s), etc., forcollimating the laser beam as it is transmitted through collimating lensL1 and through the system in a S-incident manner; a fixedspatial-frequency diffractive optical element (DOE), i.e. diffractiongrating, indicated by D1 having a beam expansion factor MI; and a fixedspatial-frequency diffractive optical element (DOE) indicated by D2,having a beam expansion factor M₂. Collectively, the collimating lens(L1), the fixed spatial-frequency DOE H1 and the fixed spatial-frequencyDOE D2 comprise a laser beam-modifying (sub)system in accordance withthe present invention. Each of the DOEs can be realized as a HOE, acomputer-generated hologram (CGHs), a surface-relief hologram, or otherdiffractive optical element.

[0127] In this embodiment, the total beam-shaping factor (M=M₁M₂) forthe laser beam modifying subsystem is less than unity (1), that isM1*M2<1, and thus the laser beam leaving the collimating lens (L1) iscompressed in one dimension. Notably, there will be many cases in whichthe beam shaping factor is less than unity, including, for example:where M1<1 and M2<1; where M1=1 and M2<1; and where M1<1 and M2=1. Inthe Beam Compression Mode, one of the cross-sectional dimensions of thelaser beam from the VLD is compressed at the output of the system to apredetermined dimension. Typically, although not necessarily, the widercross-sectional dimension of the laser beam will be the one that iscompressed. For example, if the beam is S-polarized at DOE D1, then thewidest cross-sectional dimension of the laser beam from the VLD iscompressed at the output of the system to a predetermined dimension. Ifthe beam is P-polarized, then the narrowest dimension of the laser beamfrom the VLD is compressed at the output of the system to apredetermined dimension, thereby making the laser beam even moreelliptical in cross-section.

[0128] In the laser beam producing system shown in FIG. 2A, theaspect-ratio of the output laser beam is controlled and dispersion inthe output laser beam produced therefrom eliminated for the central ray(and minimized for off-center rays) for any given beam expansion ratioat each of the DOEs, by way of selecting the right combination of anglesof incidence and diffraction for the two DOEs D1 and D2 indicated byθ_(i1), θ_(d1), θ_(i2) and θ_(d2) which, in turn, determine the properangle between the two DOEs, indicated by ρ. In this embodiment, the(x,y,z) position of the VLD is adjustable relative to lens L1 during theparameter alignment stage of the system assembly process in order to setthe focal length of the output laser beam to the desired value and toalign the VLD to the optical axis of lens L1. The (x,y,z) position ofthe VLD has no effect on dispersion except insofar as the x, y positioneffects the angle of incidence θ_(i1) at H1. If the laser beam outputfrom the VLD is not aligned along the optical axis of L1, thendispersion may not be zereod or minimized as the beam will not passthrough the DOEs are designed. In this embodiment, astigmatism in theoutput laser beam is not minimized or otherwise controlled.Consequently, there will be a number of applications to which thissystem embodiment can be put with satisfactory result.

[0129] Notably, in the embodiment of the laser beam producing systemshown in FIG. 2A, the convergence of the beam leaving collimating lensL1 must be adjusted to provide the proper image distance to the focalpoint of the system, and therefore it cannot be used to control oreliminate the astigmatism that is inherent in the laser beam leaving theVLD. In the case of Scan-Engine and like type applications, where thelaser scanning device is realized within an ultra-small volume, laserbeam astigmatism is not a problem as the increase (i.e. elongation) inspot-size in the non-scan-dimension helps reduce the problems associatedwith paper noise, described in U.S. Pat. No. 4,748,316, incorporatedherein by reference.

[0130] Second Illustrative System Embodiment Of The Laser Beam ProducingSystem Of The Present Invention

[0131] In FIG. 2B, the second illustrative embodiment of the laser beamproducing system hereof (“System Embodiment No. 2”) comprises: a laserbeam source, such as a visible laser diode (VLD), for producing a laserbeam from its junction having divergent and elliptical characteristics;a collimating lens (L1), realizable as a refractive lens e.g. a{fraction (4/35)} mm lens, a HOE, other type of DOE, a grin lens, one ormore zone plate(s), etc., for collimating the laser beam as it istransmitted through collimating lens L1 and through the system in aS-incident manner; a fixed spatial-frequency diffractive optical element(DOE), i.e. diffraction grating, indicated by D1 having a beam expansionfactor M₁; and a fixed spatial-frequency diffractive optical element(DOE), i.e. diffraction grating, indicated by D2, having a beamexpansion factor M₂; and a focusing lens L2, realizable as a refractivelens, a HOE, a DOE, a grin lens, zone plate(s) or the like, disposedafter DOE D2 for focusing the output laser beam to a desired or requiredpoint in space. Collectively, the collimating lens L1, the fixedspatial-frequency DOE D1, the fixed spatial-frequency DOE D2, andfocusing lens L2, comprise a laser beam modifying subsystem inaccordance with the present invention. Each of the DOEs can be realizedas a HOE, a CGH, a surface-relief hologram, or other diffractive opticalelement.

[0132] In this embodiment, the total beam-shaping factor (M=M₁M₂) forthe laser beam modifying subsystem is less than unity (1), that isM1*M2<1, and thus the laser beam leaving the collimating lens (L1) iscompressed in one dimension. Notably, there will be many cases in whichthe beam shaping factor is less than unity, including, for example:where M1<1 and M2<1; where M1=1 and M2<1; and where M1<1 and M2=1. Inthe Beam Compression Mode, one of the cross-sectional dimensions of thelaser beam from the VLD is compressed at the output of the system to apredetermined dimension. Typically, although not necessarily, the widercrosssectional dimension of the laser beam will be the one that iscompressed. In this embodiment, the total beam-shaping factor (M=M₁M₂)for the laser beam subsystem is less than unity (1), and thus the laserbeam leaving the collimating lens (L1) is compressed in one dimension.

[0133] In the laser beam producing system shown in FIG. 2B, theaspect-ratio of the output laser beam can be controlled and dispersionin the output laser beam produced therefrom can be eliminated (orminimized) for any given beam expansion ratio at each of the DOEs, byway of selecting the right combination of angles of incidence anddiffraction for the two DOEs D1 and D2 indicated by θ_(i1), θ_(d1),θ_(i2) and θ_(d2), which, in turn, determine the proper angle betweenthe two DOEs, indicated by ρ.

[0134] In this embodiment of the laser beam producing system, theinherent astigmatism of the laser beam leaving the VLD can be eitheradjusted or eliminated by choosing proper divergence or convergence ofthe laser beam leaving the collimating lens L1. The (x,y,z) position ofvisible laser diode VLD is adjustable relative to the lens L1 during theparameter adjustment stage of the system assembly process, in order toadjust the divergence or convergence of the beam leaving lens L1 and toalign the VLD to the optical axis of lens L1. Also, the position of lensL2 is adjustable along its optical axis relative to DOE D2 during thealignment stage of the system assembly process in order to set the focallength of the output laser beam to the desired value.

[0135] Third Illustrative System Embodiment Of The Laser Beam ProducingSystem Of The Present Invention

[0136] In FIG. 2C, the third illustrative embodiment of the laser beamproducing system hereof (“System Embodiment No. 3”) comprises: a laserbeam source, such as a visible laser diode (VLD), for producing a laserbeam from its junction; a collimating lens (L1), realizable as arefractive lens, a HOE, a DOE, a grin lens, zone plate(s) or the like,for collimating the laser beam as it is transmitted through collimatinglens L1 and through the system in a S-incident manner; a fixedspatial-frequency diffractive optical element (DOE), i.e. diffractiongrating, indicated by D1 having a beam expansion factor M1; and avariable spatial-frequency diffractive optical element (DOE) indicatedby D2, having a beam expansion factor M₂. Collectively, the collimatinglens L1, the fixed spatial-frequency DOE D1 and the variablespatial-frequency DOE D2 comprise a laser beam-modifying (sub)system inaccordance with the present invention. Each of the DOEs can be realizedas a HOE, a CGH, a surface-relief hologram, or other diffractive opticalelement.

[0137] In this embodiment, the total beam-shaping factor (M=M₁M₂) forthe laser beam modifying subsystem is less than unity (1), that isM1*M2<1, and thus the laser beam leaving the collimating lens (L1) iscompressed in one dimension. There will be many cases in which the beamshaping factor is less than unity, including, for example: where M1<1and M2<1; where M1=1 and M2<1; and where M1<1 and M2=1. In the BeamCompression Mode, one of the cross-sectional dimensions of the laserbeam from the VLD is compressed at the output of the system to apredetermined dimension. Typically, although not necessarily, the widercross-sectional dimension of the laser beam will be the one that iscompressed.

[0138] In the laser beam producing system shown in FIG. 2C, theaspect-ratio of the output laser beam can be controlled and dispersionin the output laser beam produced therefrom is eliminated (or minimized)for any given beam expansion ratio at each of the DOEs, by way ofselecting the right combination of angles of incidence and diffractionfor the two DOEs D1 and D2 indicated by θ_(il), θ_(d1), θ_(i2) andθ_(d2), which, in turn, determine the proper angle between the two DOEs,indicated by ρ.

[0139] In this embodiment of the laser beam producing system, theinherent astigmatism of the laser beam leaving the VLD is adjusted oreliminated by choosing proper divergence or convergence of the laserbeam leaving the collimating lens L1. The (x,y) position of visiblelaser diode VLD is adjustable relative to the lens L1 during theparameter adjustment stage of the system assembly process, in order toadjust the divergence or convergence of the beam leaving lens L1. The zposition of visible laser diode (VLD) is adjustable relative to the lensL1 during the parameter adjustment stage of the system assembly process,in order to align the VLD with respect to the optical axis of lens L1.Also, the position of DOE D2 is adjustable along its optical axisrelative to DOE D1 during the alignment stage of the system assemblyprocess in order to set the focal length of the output laser beam to thedesired value.

[0140] Fourth Illustrative System Embodiment Of The Laser Beam ProducingSystem Of The Present Invention

[0141] In FIG. 2D, the fourth illustrative embodiment of the laser beamproducing system hereof (“System Embodiment No. 4”) comprises: a laserbeam source, such as a visible laser diode (VLD), for producing anelliptical divergent laser beam from its junction; a collimating lens(L1), realizable as a refractive lens, a HOE, or other DOE, a grin lens,zone plate(s), etc., for collimating the laser beam as it is transmittedthrough collimating lens L1 and through the system in a S-incidentmanner; a fixed spatial-frequency diffractive optical element (DOE),i.e. diffraction grating, indicated by D1; a variable spatial-frequencydiffractive optical element (DOE) indicated by D2 and adjustably mountedto enable, during the alignment stage of the system adjustment process,the principal plane of DOE D2 to be translated along its optical axisrelative to the principal plane of DOE D1 without modifying the tiltangle therebetween; and a focusing lens (L2), realizable as a refractivelens, a HOE, a DOE, a grin lens, zone plate(s) or the like, disposedafter the second DOE D2 and having a focal length which is can beadjusted to enable the focusing of the output laser beam to somepredetermined focal point in space, during the alignment stage of thesystem assembly process. Collectively, the collimating lens L1, thefixed spatial-frequency DOE D1, the variable spatial-frequency DOE D2,and the focusing lens L2 comprise a laser beam-modifying subsystem inaccordance with the present invention. Each of the DOEs can be realizedas a HOE, a CGH, a surface-relief hologram, or other diffractive opticalelement.

[0142] In this illustrative embodiment of the optical system of thepresent invention, focusing lens L2 is disposed after the secondfocusing DOE D2 in order to provide additional optical power to theexiting laser beam. In general, lens L2 can be as a single lens whoseposition can be adjusted relative to the second DOE D2, or as a compoundlens system having a focal length that can be adjusted so as to adjustthe focal length of the output laser beam. This second opticalarrangement L2 would be useful in applications where, for example,multiple focusing HOEs as are commonly arranged on a holographicscanning disc (disclosed in application Ser. No. 08/573,949) or whereseveral different single HOEs of differing optical power were availableto be placed in the system. One of these HOEs on the disc could bepresented to the laser beam producing system hereof in the position ofDOE D2 and effectively vary the focal distance of the output laser beamabout an average focal point established by the lens L2, a process whichshall be referred to hereinafter as “delta-focusing”. Thisdelta-focusing feature yields the benefits of reduced spot aberrationsdue to the optical power of DOE D2 as well as increased modularity ofthe system.

[0143] In this embodiment, the total beam-shaping factor (M=M₁M₂) forthe laser beam modifying subsystem is less than unity (1), that isM1*M2<1, and thus the laser beam leaving the collimating lens (L1) iscompressed in one dimension. There will be many cases in which the beamshaping factor is less than unity, including, for example: where M1<1and M2<1; where M1=1 and M2<1; and where M1<1 and M2=1. In the BeamCompression Mode, one of the cross-sectional dimensions of the laserbeam from the VLD is compressed at the output of the system to apredetermined dimension. Typically, although not necessarily, the widercross-sectional dimension of the laser beam will be the one that iscompressed.

[0144] In the laser beam producing system shown in FIG. 2D, theaspect-ratio of the output laser beam can be controlled and dispersionin the output laser beam eliminated (or minimized) for any given beamexpansion or beam compression ratio at each of the DOEs, by selectingthe right combination of angles of incidence and diffraction for the twoDOEs D1 and D2 indicated by θ_(i1), θ_(d1), θ_(i2) and θ_(d2), which, inturn, determine the proper angle between the two DOEs, indicated by ρ.

[0145] In this embodiment of the laser beam producing system, theinherent astigmatism of the laser beam leaving the VLD is adjusted oreliminated by choosing proper divergence or convergence of the laserbeam leaving the collimating lens L1. The (x,y) position of visiblelaser diode VLD is adjustable relative to the lens L1 during theparameter adjustment stage of the system assembly process, in order toadjust the divergence or convergence of the beam leaving lens L1. The zposition of visible laser diode VLD is adjustable relative to the lensL1 during the parameter adjustment stage of the system assembly process,in order to align the VLD relative to the optical axis of lens L1. Also,the position of second lens L2 is adjustable along its optical axisrelative to DOE D2 during the alignment stage of the system assemblyprocess. The function of this second lens L2 is to set the average focallength of the output laser beam to the desired value for use by thedelta-focusing subsystem. Fifth Illustrative System Embodiment Of TheLaser Beam Producing System Of The Present Invention In FIG. 2E, thefifth illustrative embodiment of the laser beam producing system hereof(“System Embodiment No. 5”) comprises: a laser beam source, such as avisible laser diode (VLD), for producing a laser beam from its junction;a collimating (non-focusing) lens (L1), realizable as a refractive lens,a HOE or other DOE, a grin lens, zone plate(s), etc., for collimatingthe laser beam as it is transmitted through collimating lens L1 andthrough the system in a P-incident manner; a fixed spatial-frequencydiffractive optical element (DOE), i.e. diffraction grating, indicatedby D1; and a fixed spatial-frequency diffractive optical element (DOE)indicated by D2. Collectively, the collimating lens L1, the fixedspatial-frequency DOE D1 and the fixed spatial-frequency DOE D2 comprisea laser beam-modifying (sub)system in accordance with the presentinvention. Each of the DOEs can be realized as a HOE, a CGH, asurface-relief hologram, or other diffractive optical element.

[0146] In this embodiment, the total beam-shaping factor (M=M₁M₂) forthe laser beam modifying subsystem is greater than unity (1), that isM1*M2>1, and thus the laser beam leaving the collimating lens (L1) isexpanded in one dimension. There will be many cases in which the beamshaping factor is greater than unity, including, for example: where M1>1and M2>1; where M1=1 and M2>1; and where M1>1 and M2=1. In the BeamExpansion Mode, one of the cross-sectional dimensions of the laser beamfrom the VLD is expanded at the output of the system to a predetermineddimension. Typically, although not necessarily, the narrowercross-sectional dimension of the laser beam will be the one that isexpanded.

[0147] In the laser beam producing system shown in FIG. 2E, theaspect-ratio of the output laser beam can be controlled and dispersionin the output laser beam produced therefrom is eliminated (or minimized)for any given beam expansion ratio at each of the DOEs, by way ofselecting the right combination of angles of incidence and diffractionfor the two DOEs D1 and D2 indicated by θ_(i1), θ_(d1), θ_(i2) andθ_(d2), which, in turn, determine the proper angle between the two DOEs,indicated by ρ.

[0148] In this embodiment, the (x,y) position of the VLD is adjustablerelative to lens L1 during the parameter alignment stage of the systemassembly process in order to set the focal length of the output laserbeam to the desired value. The z position of the VLD is adjustablerelative to lens L1 during the parameter alignment stage of the systemassembly process in order to align the VLD to the optical axis of lensL1.

[0149] Notably, in the embodiment of the laser beam producing systemshown in FIG. 2E, the convergence of the beam leaving collimating lensL1 must be adjusted to provide the proper image distance to the focalpoint of the system, and therefore it cannot be used to control oreliminate the astigmatism that is inherent in the laser beam leaving theVLD. In the case of Scan-Engine and like type applications, where thelaser scanning device is realized within an ultra-small volume, laserbeam astigmatism is not a problem as the increase (i.e. elongation) inspot-size in the non-scan-dimension helps reduce the problems associatedwith paper noise, described in U.S. Pat. No. 4,748,316, supra.

[0150] Sixth Illustrative System Embodiment Of The Laser Beam ProducingSystem Of The Present Invention

[0151] In FIG. 2F, the sixth illustrative embodiment of the laser beamproducing system hereof (“System Embodiment No. 6”) comprises: a laserbeam source, such as a visible laser diode (VLD), for producing a laserbeam from its junction; a collimating lens (L1), realizable as arefractive lens, a HOE or other DOE, a grin lens, zone plate(s), etc.,for collimating the laser beam as it is transmitted through collimatinglens L1 and through the system in a P-incident manner; a fixedspatial-frequency diffractive optical element (DOE), i.e. diffractiongrating, indicated by D1; a fixed spatial-frequency diffractive opticalelement (DOE) indicated by D2; and a focusing lens (L2), realizable as arefractive lens, a HOE, a DOE, a grin lens, zone plate(s) or the like,disposed after the second DOE D2 for focusing the output laser beam tosome point in space. Collectively, the collimating lens L1, the fixedspatial-frequency DOE D1, the fixed spatial-frequency DOE D2, andfocusing lens L2 comprise a laser beam-modifying (sub)system inaccordance with the present invention. Each of the DOEs can be realizedas a HOE, a CGH, a surface-relief hologram, or other diffractive opticalelement.

[0152] In this embodiment, the total beam-shaping factor (M=M1M₂) forthe laser beam modifying subsystem is greater than unity (1), that isM1*M2>1, and thus the laser beam leaving the collimating lens (L1) isexpanded in one dimension. There will be many cases in which the beamshaping factor is greater than unity, including, for example: where M1>1and M2>1; where M1=1 and M2>1; and where M1>1 and M2=1. In the BeamExpansion Mode, one of the cross-sectional dimensions of the laser beamfrom the VLD is expanded at the output of the system to a predetermineddimension. Typically, although not necessarily, the narrowercross-sectional dimension of the laser beam will be the one that isexpanded.

[0153] In the laser beam producing system shown in FIG. 2F, aspect-ratiocontrol is achieved and dispersion in the output laser beam iseliminated (or minimized) for any given beam expansion ratio at each ofthe DOEs, by way of selecting the right combination of angles ofincidence and diffraction for the two DOEs D1 and D2 indicated byθ_(i1), θ_(d1), θ_(i2) and θ_(d2) which, in turn, determine the properangle between the two DOEs, indicated by ρ.

[0154] In this embodiment of the laser beam producing system, theinherent astigmatism of the laser beam leaving the VLD is eitheradjusted or eliminated by choosing proper divergence or convergence ofthe laser beam leaving the collimating lens L1. The (x,y) position ofvisible laser diode VLD is adjustable relative to the lens L1 during theparameter adjustment stage of the system assembly process in order toadjust the divergence or convergence of the beam leaving lens L1. The zposition of visible laser diode VLD is adjustable relative to the lensL1 during the parameter adjustment stage of the system assembly processin order to align the VLD to the optical axis of lens L1. Setting thefocal length of output laser beam is achieved by adjusting the positionof lens L2 relative to DOE D2 during the alignment stage of the assemblyprocess.

[0155] Seventh Illustrative System Embodiment Of The Laser BeamProducing System Of The Present Invention

[0156] In FIG. 2G, the seventh illustrative embodiment of the laser beamproducing system hereof (“System Embodiment No. 7”) comprises: a laserbeam source, such as a visible laser diode (VLD), for producing a laserbeam from its junction; a collimating lens (L1), realizable as arefractive lens, HOE or other DOE, a grin lens, zone plate(s), etc., forcollimating the laser beam as it is transmitted through collimating lensL1 and through the system in a P-incident manner; a fixedspatial-frequency diffractive optical element (DOE), i.e. diffractiongrating, indicated by D1; and a variable spatial-frequency diffractiveoptical element (DOE) indicated by D2, which can be translated along theoptical axis relative to the principal plane of DOE DI during thealignment stage of the system assembly process. Collectively, thecollimating lens L1, the fixed spatial-frequency DOE D1 and the variablespatial-frequency DOE D2 comprise a laser beam-modifying (sub)system inaccordance with the present invention. Each of the DOEs can be realizedas a DOE, a CGH, a surface-relief hologram, or other diffractive opticalelement.

[0157] In this embodiment, the total beam-shaping factor (M=M₁M₂) forthe laser beam modifying subsystem is greater than unity (1), that isM1*M2>1, and thus the laser beam leaving the collimating lens (L1) isexpanded in one dimension. There will be many cases in which the beamshaping factor is greater than unity, including, for example: where M1>1and M2>1; where M1=1 and M2>1; and where M1>1 and M2=1. In the BeamExpansion Mode, one of the cross-sectional dimensions of the laser beamfrom the VLD is expanded at the output of the system to a predetermineddimension. Typically, although not necessarily, the narrowercross-sectional dimension of the laser beam will be the one that isexpanded.

[0158] In the laser beam producing system shown in FIG. 2G, aspect-ratiocontrol is achieved and dispersion in the output laser beam iseliminated (or minimized) for any given beam expansion ratio at each ofthe DOEs, by way of selecting the right combination of angles ofincidence and diffraction for the two DOEs D1 and D2 indicated byθ_(i1), θ_(d1), θ_(i2) and θ_(d2), which, in turn, determine the properangle between the two DOEs, indicated by ρ.

[0159] In this embodiment of the laser beam producing system, theinherent astigmatism of the laser beam leaving the VLD is eitheradjusted or eliminated by choosing proper divergence or convergence ofthe laser beam leaving the collimating lens L1. The (x,y) position ofvisible laser diode VLD is adjustable relative to the lens L1 during theparameter adjustment stage of the system assembly process, in order toadjust the divergence or convergence of the beam leaving lens L1. The zposition of visible laser diode VLD is adjustable relative to the lensL1 during the parameter adjustment stage of the system assembly processin order to align the VLD to the optical axis of lens L1. Also, theposition of DOE D2 is adjustable along its optical axis relative to DOED1 during the alignment stage of the system assembly process in order toset the focal length of the output laser beam to the desired value.

[0160] Eighth Illustrative System Embodiment Of The Laser Beam ProducingSystem Of The Present Invention

[0161] In FIG. 2H, the eighth illustrative embodiment of the laser beamproducing system hereof (“System Embodiment No. 8”) comprises: a laserbeam source, such as a visible laser diode (VLD); a collimating lens(L1) realizable as a refractive lens, a HOE, a CGH or other DOE, a grinlens, zone plate(s), etc., for collimating the laser beam as it istransmitted through collimating lens L1 and through the system in aP-incident manner; a fixed spatial-frequency diffractive optical element(DOE), i.e. diffraction grating, indicated by D1; a variablespatial-frequency diffractive optical element (DOE) indicated by D2,adjustably mounted relative to DOE D1; and a focusing lens (L2),realizable as a refractive lens, a HOE, a DOE, grin lens, zone plate(s)or the like, disposed after the second DOE D2, and adjustably mountedrelative thereto, for focusing the output laser beam to some point inspace. Collectively, the collimating lens L1, the fixedspatial-frequency DOE D1, the variable spatial-frequency DOE D2 andfocusing lens L2 comprise a laser beam-modifying (sub)system inaccordance with the present invention. Each of the DOEs can be realizedas a HOE, a CGH, a surface-relief hologram, or other diffractive opticalelement.

[0162] In this illustrative embodiment of the optical system of thepresent invention, focusing lens L2 is disposed after the secondfocusing DOE D2 in order to provide additional optical power to theexiting laser beam. This optical arrangement would be useful inapplications employing delta-focusing. This delta-focusing yields thebenefits of reduced spot aberrations due to the optical power of DOE D2as well as increased modularity of the system.

[0163] In this embodiment, the total beam-shaping factor (M=M₁M₂) forthe laser beam modifying subsystem is greater than unity (1), that isM1*M2>1, and thus the laser beam leaving the collimating lens (L1) isexpanded in one dimension. There will be many cases in which the beamshaping factor is greater than unity, including, for example: where M1>1and M2>1; where M1=1 and M2>1; and where M1>1 and M2=1. In the BeamExpansion Mode, one of the cross-sectional dimensions of the laser beamfrom the VLD is expanded at the output of the system to a predetermineddimension. Typically, although not necessarily, the narrowercross-sectional dimension of the laser beam will be the one that isexpanded.

[0164] In the laser beam producing system shown in FIG. 2H, aspect-ratiocontrol is achieved and dispersion in the output laser beam iseliminated (or minimized) for any given beam expansion ratio at each ofthe DOEs, by way of selecting the right combination of angles ofincidence and diffraction for the two DOEs D1 and D2 indicated byθ_(i1), θ_(d1), θ_(i2) and θ_(d2) which in turn, determine the properangle between the two DOEs, indicated by ρ.

[0165] In this embodiment of the laser beam producing system, theinherent astigmatism of the laser beam leaving the VLD is eitheradjusted or eliminated by choosing proper divergence or convergence ofthe laser beam leaving the collimating lens L1. The (x,y) position ofvisible laser diode VLD is adjustable relative to the lens L1 during theparameter adjustment stage of the system assembly process, in order toadjust the divergence or convergence of the beam leaving lens L1. The zposition of visible laser diode VLD is adjustable relative to the lensL1 during the parameter adjustment stage of the system assembly process,in order to align the VLD to the optical axis of lens L1. Also, theposition of lens L2 is adjustable along its optical axis relative to DOED2 during the alignment stage of the system assembly process in order toset the average focal length of the output laser beam to the desiredvalue for use by the delta-focusing system.

[0166] Ninth Illustrative System Embodiment Of The Laser Beam ProducingSystem Of The Present Invention

[0167] In FIG. 21, the ninth illustrative embodiment of the laser beamproducing system hereof (“System Embodiment No. 9”) comprises: a laserbeam source, such as a visible laser diode (VLD), for producing a laserbeam from its junction; a collimating lens (L1), realizable as arefractive lens, a HOE, CGH or other DOE, a grin lens, zone plate(s),etc., for collimating the laser beam as it is transmitted throughcollimating lens L1 and through the system in an S-incident manner; afixed spatial-frequency diffractive optical element (DOE), i.e.diffraction grating, indicated by D1; a fixed spatial-frequencydiffractive optical element (DOE) indicated by D2; and a focusing lens(L2), realizable as a refractive lens, holographic optical element(HOE), diffractive optical element (DOE), grin lens, zone plate(s) orthe like, disposed between DOE D1 and DOE D2 and adjustably translatablealong its optical axis for focusing the output laser beam to some pointin space. Collectively, the collimating lens L1, the fixedspatial-frequency DOE D1, the fixed spatial-frequency DOE D2, andfocusing lens L2 comprise a laser beam-modifying (sub)system inaccordance with the present invention. Each of the DOEs can be realizedas a HOE, a CGH, a surface-relief hologram, or other diffractive opticalelement.

[0168] In this embodiment, the total beam-shaping factor (M=M₁M₂) forthe laser beam modifying subsystem is less than unity (1), that isM1*M2<1, and thus the laser beam leaving the collimating lens (L1) iscompressed in one dimension. Notably, there will be many cases in whichthe beam shaping factor is less than unity, including, for example:where M1<1 and M2<1; where M1=1 and M2<1; and where M1<1 and M2=1. Inthe Beam Compression Mode, one of the cross-sectional dimensions of thelaser beam from the VLD is compressed at the output of the system to apredetermined dimension. Typically, although not necessarily, the widercross-sectional dimension of the laser beam will be the one that iscompressed.

[0169] In the laser beam producing system shown in FIG. 2I, aspect-ratiocontrol is achieved and dispersion in the output laser beam iseliminated (or minimized) for any given beam expansion or beamcompression ratio at each of the DOEs, by way of selecting the rightcombination of angles of incidence and diffraction for the two DOEs D1and D2 indicated by θ_(i1), θ_(d1), θ_(i2) and θ_(d2), which, in turn,determine the proper angle between the two DOEs, indicated by ρ.

[0170] In this embodiment of the laser beam producing system, lenses L1and L2 are chosen such that the desired focus is achieved and theinherent astigmatism of the laser beam leaving the VLD is eitheradjusted or eliminated. Neither lens L1 nor L2 independently set theastigmatism nor the focus. Rather the combined set of lenses produce thecombined result.

[0171] The (z) position of visible laser diode VLD is adjustablerelative to the lens L1 during the parameter adjustment stage of thesystem assembly process, in order to adjust the divergence orconvergence of the beam leaving lens L1 to produce a predeterminedamount of astigmatism at a predetermined distance. The (x,y) position ofvisible laser diode VLD is adjustable relative to the lens L1 during theparameter adjustment stage of the system assembly process, in order toalign the VLD to the optical axis of lens L1. Also, the position of lensL2 is adjustable along its optical axis between DOE D1 and DOE D2 duringthe alignment stage of the system assembly process in order to set thedesired focus as well as the desired amount of astigmatism of the outputlaser beam.

[0172] Tenth Illustrative System Embodiment Of The Laser Beam ProducingSystem Of The Present Invention

[0173] In FIG. 2J, the tenth illustrative embodiment of the laser beamproducing system hereof (“System Embodiment No. 10”) comprises: a laserbeam source, such as a visible laser diode (VLD), for producing a laserbeam from its junction; a collimating lens (L1), realizable as arefractive lens, a HOE, CGH or other DOE, a grin lens, zone plate(s),etc., for collimating the laser beam as it is transmitted throughcollimating lens L1 and through the system in a S-incident manner; afixed spatial-frequency diffractive optical element (DOE), i.e.diffraction grating, indicated by D1; a variable spatial-frequencydiffractive optical element (DOE) indicated by D2, adjustablytranslatable relative to the principal plane of DOE D1 during thealignment stage of the system assembly process; and a focusing lens(L2), realizable as a refractive lens, a HOE, a DOE, a grin lens, zoneplate(s) or the like, disposed between DOE D1 and DOE D2 and adjustablytranslatable along its optical axis during the parameter alignment stageof the system assembly process for focusing the output laser beam tosome point in space. Collectively, the collimating lens L1, the fixedspatial-frequency DOE D1, the variable spatial-frequency DOE D2, andfocusing lens L2 comprise a laser beam-modifying (sub)system inaccordance with the present invention. Each of the DOEs can be realizedas a HOE, a CGH, a surface-relief hologram, or other diffractive opticalelement.

[0174] In this illustrative embodiment of the optical system of thepresent invention, focusing lens L2 is disposed between DOE D1 and DOED2 in order to provide additional optical power to the exiting laserbeam. This optical arrangement would be useful in applications employingdelta-focusing. This delta-focusing yields the benefits of reduced spotaberrations due to the optical power of DOE D2 as well as increasedmodularity of the system.

[0175] In this embodiment, the total beam-shaping factor (M=M₁M₂) forthe laser beam modifying subsystem is less than unity (1), that isM1*M2<1, and thus the laser beam leaving the collimating lens (L1) iscompressed in one dimension. Notably, there will be many cases in whichthe beam shaping factor is less than unity, including, for example:where M1<1 and M2<1; where M1=1 and M2<1; and where M1<1 and M2=1. Inthe Beam Compression Mode, one of the cross-sectional dimensions of thelaser beam from the VLD is compressed at the output of the system to apredetermined dimension. Typically, although not necessarily, the widercross-sectional dimension of the laser beam will be the one that iscompressed.

[0176] In the laser beam producing system shown in FIG. 2J, beamaspect-ratio control is achieved and dispersion in the output laser beamis eliminated (or minimized) for any given beam expansion or beamcompression ratio at each of the DOEs, by way of selecting the rightcombination of angles of incidence and diffraction for the two DOEs D1and D2 indicated by θ_(i1), θ_(d1), θ_(i2) and θ_(d2) which, in turn,determine the proper angle between the two DOEs, indicated by ρ.

[0177] In this embodiment of the laser beam producing system, theinherent astigmatism of the laser beam leaving the VLD can be eitheradjusted or eliminated by choosing proper divergence or convergence ofthe laser beam leaving the collimating lens L1. The (x,y) position ofvisible laser diode VLD is adjustable relative to the lens D1 during theparameter adjustment stage of the system assembly process, in order toadjust the divergence or convergence of the beam leaving lens L1. The(z) position of visible laser diode VLD is adjustable relative to thelens L1 during the parameter adjustment stage of the system assemblyprocess, in order to align the VLD to the optical axis of lens L1. Also,the position of lens L2 is adjustable along its optical between DOE D1and DOE D2 during the alignment stage of the system assembly process inorder to set the average focal length of the output laser beam to thedesired value for use by the delta-focusing system.

[0178] Eleventh Illustrative System Embodiment Of The Laser BeamProducing System Of The Present Invention

[0179] In FIG. 2K, the eleventh illustrative embodiment of the laserbeam producing system hereof (“System Embodiment No. 11”) comprises: alaser beam source, such as a visible laser diode (VLD), for producing alaser beam from its junction; a collimating lens (L1), realizable as arefractive lens, a HOE or other DOE, a grin lens, zone plate(s), etc.,for collimating the laser beam as it is transmitted through collimatinglens L1 and through the system in a P-incident manner; a fixedspatial-frequency diffractive optical element (DOE), i.e. diffractiongrating, indicated by D1; a fixed spatial-frequency diffractive opticalelement (DOE) indicated by D2; and a focusing lens (L2), realizable as arefractive lens, holographic optical element (HOE), diffractive opticalelement (DOE), grin lens, zone plate(s) or the like, between DOE D1 andDOE D2 and adjustably translatable along its optical axis during thealignment stage of the system assembly process for focusing the outputlaser beam to some point in space. Collectively, the collimating lensL1, the fixed spatial-frequency DOE D1, the fixed spatial-frequency DOED2, and the focusing lens L2 comprise a laser beam-modifying (sub)systemin accordance with the present invention. Each of the DOEs can berealized as a HOE, a CGH, a surface-relief hologram, or otherdiffractive optical element.

[0180] In this embodiment, the total beam-shaping factor (M=M₁M₂) forthe laser beam modifying subsystem is greater than unity (1), that isM1*M2>1, and thus the laser beam leaving the collimating lens (L1) isexpanded in one dimension. There will be many cases in which the beamshaping factor is greater than unity, including, for example: where M1>1and M2>1; where M1=1 and M2>1; and where M1>1 and M2=1. In the BeamExpansion Mode, one of the cross-sectional dimensions of the laser beamfrom the VLD is expanded at the output of the system to a predetermineddimension. Typically, although not necessarily, the narrowercross-sectional dimension of the laser beam will be the one that isexpanded.

[0181] In the laser beam producing system shown in FIG. 2K, beamaspect-ratio is controlled and dispersion in the output laser beam iseliminated (or minimized) for any given beam expansion ratio at each ofthe DOEs, by way of selecting the right combination of angles ofincidence and diffraction for the two DOEs D1 and D2 indicated byθ_(i1), θ_(d1), θ_(i2) and θ_(d2), which, in turn determine the properangle between the two DOEs, indicated by ρ.

[0182] In this embodiment of the laser beam producing system, lenses L1and L2 are chosen such that the desired focus is achieved and theinherent astigmatism of the laser beam leaving the VLD is eitheradjusted or eliminated. Neither lens L1 nor L2 independently set theastigmatism nor the focus. Rather the combined set of lenses produce thecombined result.

[0183] The (z) position of visible laser diode VLD is adjustablerelative to the lens L1 during the parameter adjustment stage of thesystem assembly process, in order to adjust the divergence orconvergence of the beam leaving lens L1 to produce a predeterminedamount of astigmatism at a predetermined distance. The (x,y) position ofvisible laser diode VLD is adjustable relative to the lens L1 during theparameter adjustment stage of the system assembly process, in order toalign the VLD to the optical axis of lens L1. Also, the position of lensL2 is adjustable along its optical axis between DOE D1 and DOE D2 duringthe alignment stage of the system assembly process in order to set thedesired focus as well as the desired amount of astigmatism of the outputlaser beam.

[0184] Twelfth Illustrative System Embodiment Of The Laser BeamProducing System Of The Present Invention

[0185] In FIG. 2L, the twelfth illustrative embodiment of the laser beamproducing system hereof (“System Embodiment No. 12”) comprises: a laserbeam source, such as a visible laser diode (VLD), for producing a laserbeam from its junction; a collimating lens (L1), realizable as arefractive lens, a HOE, CGH or other DOE, a grin lens, zone plate(s),etc., for collimating the laser beam as it is transmitted throughcollimating lens L1 and through the system in a P-incident manner; afixed spatial-frequency diffractive optical element (DOE), i.e.diffraction grating, indicated by D1; a variable spatial-frequencydiffractive optical element (DOE) indicated by D2, adjustablytranslatable relative to the principal plane of DOE D1 during thealignment stage of the system assembly process; and a focusing lens(L2), realizable as a refractive lens, a HOE, a CGH or other a DOE, agrin lens, zone plate(s) or the like, disposed between DOE D1 and DOE D2and adjustably translatable along its optical axis during the parameteralignment stage of the system assembly process for focusing the outputlaser beam to some point in space. Collectively, the collimating lens(L1), the fixed spatial-frequency DOE (D1) and the variablespatial-frequency DOE (D2) comprise a laser beam-modifying (sub)systemin accordance with the present invention. Each of the DOEs can berealized as a HOE, a CGH, a surface-relief hologram, or otherdiffractive optical element.

[0186] In this illustrative embodiment of the optical system of thepresent invention, focusing lens L2 is disposed between DOE D1 and DOED2 in order to provide additional optical power to the exiting laserbeam. This optical arrangement would be useful in applications employingdelta-focusing. This delta-focusing yields the benefits of reduced spotaberrations due to the optical power of DOE D2 as well as increasedmodularity of the system.

[0187] In this embodiment, the total beam-shaping factor (M=M₁M₂) forthe laser beam modifying subsystem is greater than unity (1), that isM1*M2>1, and thus the laser beam leaving the collimating lens (L1) isexpanded in one dimension. There will be many cases in which the beamshaping factor is greater than unity, including, for example: where M1>1and M2>1; where M1=1 and M2>1; and where M1>1 and M2=1. In the BeamExpansion Mode, one of the cross-sectional dimensions of the laser beamfrom the VLD is expanded at the output of the system to a predetermineddimension. Typically, although not necessarily, the narrowercross-sectional dimension of the laser beam will be the one that isexpanded.

[0188] In the laser beam producing system shown in FIG. 2L, beamaspect-ratio control is achieved and dispersion in the output laser beamis eliminated (or minimized) for any given beam expansion ratio at eachof the DOEs, by way of selecting the right combination of angles ofincidence and diffraction for the two DOEs D1 and D2 indicated byθ_(i1), θ_(d1), θ_(i2) and θ_(d2), which, in turn, determine the properangle between the two DOEs, indicated by ρ.

[0189] In this embodiment of the laser beam producing system, theinherent astigmatism of the laser beam leaving the VLD can be eitheradjusted or eliminated by choosing proper divergence or convergence ofthe laser beam leaving the collimating lens L1. The (x,y) position ofvisible laser diode VLD is adjustable relative to the lens L1 during theparameter adjustment stage of the system assembly process, in order toadjust the divergence or convergence of the beam leaving lens L1. The(z) position of visible laser diode VLD is adjustable relative to thelens L1 during the parameter adjustment stage of the system assemblyprocess, in order to align the VLD to the optical axis of lens L1. Also,the position of lens L2 is adjustable along its optical axis between DOED1 and DOE D2 during the alignment stage of the system assembly processin order to set the average focal length of the output laser beam to thedesired value for use by the delta-focusing system.

[0190] Thirteenth Illustrative System Embodiment Of The Laser BeamProducing System Of The Present Invention

[0191] In FIG. 2M, the thirteenth illustrative embodiment of the laserbeam producing system hereof (“System Embodiment No. 13”) comprises: alaser beam source, such as a visible laser diode (VLD), for producing alaser beam from its junction; an imaging lens (L1), realizable as arefractive lens, a HOE or other DOE, a grin lens, zone plate(s), etc.,for imaging the laser source to the focal distance as it is transmittedthrough imaging lens L1 and through the system in a S-incident manner; afixed spatial-frequency diffractive optical element (DOE), i.e.diffraction grating, indicated by D1; and a fixed spatial-frequencydiffractive optical element (DOE) indicated by D2. Collectively, thecollimating lens L1, the fixed spatial-frequency DOE D1 and the fixedspatial-frequency DOE D2 comprise a laser beam-modifying (sub)system inaccordance with the present invention. Each of the DOEs can be realizedas a HOE, a CGH, a surface-relief hologram, or other diffractive opticalelement.

[0192] In this embodiment, the total beam-shaping factor (M=M₁M₂) forthe laser beam modifying subsystem is less than unity (1), that isM1*M2<1, and thus the laser beam leaving the collimating lens (L1) iscompressed in one dimension. Notably, there will be many cases in whichthe beam shaping factor is less than unity, including, for example:where M1<1 and M2<1; where M1=1 and M2<1; and where M1<1 and M2=1. Inthe Beam Compression Mode, one of the cross-sectional dimensions of thelaser beam from the VLD is compressed at the output of the system to apredetermined dimension. Typically, although not necessarily, the widercross-sectional dimension of the laser beam will be the one that iscompressed.

[0193] In the laser beam producing system shown in FIG. 2M, beamaspect-ratio control is achieved and dispersion in the output laser beamis eliminated (or minimized) for any given i beam expansion ratio ateach of the DOES, by way of selecting the right combination of angles ofincidence and diffraction for the two DOEs D1 and D2 indicated byθ_(i1), θ_(d1), θ_(i2) and θ_(d2) which, in turn, determine the properangle between the two DOEs previously defined hereinabove.

[0194] Notably, in this embodiment of the laser beam producing system,the convergence of the beam leaving focusing lens L1 need not beadjusted to provide the proper image distance to the focal point of thesystem, and therefore it can be used to control or eliminate theastigmatism that is inherent in the laser beam leaving the VLD. Thisembodiment of the laser beam producing system will be useful inapplications where astigmatism inherent in the laser beam leaving theVLD must be corrected or eliminated, and there is no need to focus theoutput laser beam to any particular focal distance using the opticsassociated with the laser beam producing system.

[0195] Fourteenth Illustrative System Embodiment Of The Laser BeamProducing System Of The Present Invention

[0196] In FIG. 2N, the fourteenth illustrative embodiment of the laserbeam producing system thereof (“System Embodiment No. 14”) comprises: alaser beam source, such as a visible laser diode (VLD), for producing alaser beam from its junction; a focusing (non-collimating) lens (L1),realizable as a refractive lens, a HOE, CGH or other DOE, a grin lens,zone plate(s), etc., for focusing the laser beam as it is transmittedthrough focusing lens L1 and through the system in a P-incident manner;a fixed spatial-frequency diffractive optical element (DOE), i.e.diffraction grating, indicated by D1; and a fixed spatial-frequencydiffractive optical element (DOE) indicated by D2. Collectively, thefocusing lens L1, the fixed spatial-frequency DOE DI and the fixedspatial-frequency DOE D2 comprise a laser beam-modifying subsystem inaccordance with the present invention. Each of the DOEs can be realizedas a HOE, a CGH, a surface-relief hologram, or other diffractive opticalelement.

[0197] In this embodiment, the total beam-shaping factor (M=M₁M₂) forthe laser beam modifying subsystem is greater than unity (1), that isM1*M2>1, and thus the laser beam leaving the collimating lens (L1) isexpanded in one dimension. There will be many cases in which the beamshaping factor is greater than unity, including, for example: where M1>1and M2>1; where M1=1 and M2>1; and where M1>1 and M2=1. In the BeamExpansion Mode, one of the cross-sectional dimensions of the laser beamfrom the VLD is expanded at the output of the system to a predetermineddimension. Typically, although not necessarily, the narrowercross-sectional dimension of the laser beam will be the one that isexpanded.

[0198] In the laser beam producing system shown in FIG. 2N, beamaspect-ratio control and dispersion in the output laser beam iseliminated (or minimized) for any given beam expansion ratio at each ofthe DOEs, by way of selecting the right combination of angles ofincidence and diffraction for the two DOEs D1 and D2 indicated byθ_(i1), θ_(d1), θ_(i2) and θ_(d2), which, in turn, determine the properangle between the two DOEs, indicated by ρ.

[0199] In System Embodiment No. 14 shown in FIG. 2N, the convergence ofthe beam leaving focusing lens L1 need not be adjusted to provide theproper image distance to the focal point of the system, and therefore itcan be used to control or eliminate the astigmatism that is inherent inthe laser beam leaving the VLD. This embodiment of the laser beamproducing system will be useful in applications where astigmatisminherent in the laser beam leaving the VLD must be corrected oreliminated, and there is no need to focus the output laser beam to anyparticular focal distance using the optics associated with the laserbeam producing system.

[0200] In each of the fourteen illustrative embodiments describedhereinabove, it is preferred that optical elements L1 and L2 haveaxially symmetric optical properties (i.e. lenses L1 and L2 arestigmatic optical elements). In the preferred embodiments, where L1 andL2 are both refractive lenses, the lens surface profiles should beaxially symmetric in order to allow for the use of both spheric andaspheric lenses. In most cases, the sub-system consisting of the VLD andlens L1, performs outside of the realm of paraxial optics; thereforelens L1 will typically be aspheric in order to minimize the sphericalaberration common in non-paraxial systems. Also in most cases, the useof lens L2 typically satisfies the requirements of paraxial analysis;therefore, use of a spheric lens for this optical element is usuallyacceptable.

[0201] A major advantage of using an optical element with axial symmetryto realize lens L1 is that it is then be possible to use diffractiveoptics to modify (e.g. correct or eliminate) astigmatism in the outputlaser beam. Notably, if one were to realize lens L1 using an opticalelement not having axial symmetry, then diffractive elements (e.g. DOEsD1 and D2) could no longer be used to eliminate or correct astigmatismin the output laser beam, and that cylindrical or toroidal lenses wouldbe required for astigmatism control or elimination. Notably, there arenumber of important advantages obtained when using diffractive optics(rather than astigmatic refractive optics) to correct or eliminateastigmatism in the output laser beam astigmatism, namely: (1)simplification of the manufacture of the refractive optics (L1) as wellas the diffractive optics (D1 and D2); (2) reduction in the cost ofoptical elements; and (3) simplification of parameter alignment duringthe assembly process.

[0202] Methods for Designing Laser Beam Producing Systems of theIllustrative System Embodiments of the Present Invention Where FocusControl is Desired But Neither Astigmatism Correction nor Delta-Focusingare Required: System Embodiments Nos. (1) & (5)

[0203] System Embodiment Nos. (1) and (5) of the laser beam producingsystem of the present invention can be designed using thebelow-described design methodology, wherein the steps thereof are setforth in FIGS. 3A1 through 3A3.

[0204] As indicated at Block A in FIG. 3A, the first step in the designmethod involves establishing end-user requirements for the laser beamproducing module under design. In bar code symbol scanning applications,where the laser beam output from the system under design is to be usedto scan the elements of bar code symbols, such end-user requirementswill typically include, for example, the working distance from thescanner, the depth of field of the scanning system, the type of bar codesymbols that the laser beam must read, the minimal width of the elementsin the bar code symbols, etc.

[0205] As indicated at Block B, the second step in the design methodinvolves determining the necessary spot-size, aspect-ratio and waistdimensions of the output laser beam in order to scan the desired barcode determined during step (1) described at Block A.

[0206] As indicated at Block C, the third step in the design methodinvolves determining the module focal distance, f_(module), that willprovide the desired depth of field for the end-user scanning system atthe desired working distance.

[0207] As indicated at Block D in FIG. 3A1, the fourth step in thedesign method involves using a Gaussian beam propagation model todetermine the required beam size and aspect-ratio leaving the laser beamproducing system. Notably, the steps at Blocks B, C and D are somewhatinterconnected inasmuch as the spot-size, depth-of-field, and focaldistance of the output laser beam, are all aspects of Gaussian beampropagation. The values of each of these parameters have an effect onthe other parameters. Therefore, it is understood that the order inwhich such parameters are determined, may be different from embodimentto embodiment.

[0208] As indicated at Block E in FIG. 3A2, the fifth step in the designmethod involves choosing an acceptable laser source (e.g. a VLD). In anideal world, criteria for acceptability may include limits on beamdivergence and amount of astigmatism, as well as aspect ratio,wavelength, and bandwidth. However, in practice, such criteria will besatisfied by ensuring that the aspect ratio of the beam leaving the VLDis not too large for compression by the DOE-based subsystem.

[0209] As indicated at Block F in FIG. 3A2, the sixth step in the designmethod involves determining an appropriate value for the beam-shapingfactors of DOEs D1 and D2 which ensures that the aspect-ratio of thebeam entering the laser beam-modifying subsystem (D1 and D2) from theVLD is sufficiently modified so that output laser beam has the desiredaspect ratio determined at Block D described above. Notably, thebeam-shaping factor M (also called the expansion ratio), defined asM=M₁M₂, provides beam compression within the laser beam modifyingsubsystem when M<1, and provides beam expansion within the laser beammodifying subsystem when M>1.

[0210] As indicated at Block G in FIG. 3A2, the seventh step in thedesign method involves using the beam-shaping factor determined at BlockF, to determine the design angles, θ_(i1), θ_(d1), θ_(i2) θ_(d2)(expressed at the reconstruction/design wavelength, λ_(R)) for the twoDOEs D1 and D2, which provides an optical subsystem wherein the laserbeam output from the second DOE D2 thereof has (1) effectively zero netbeam dispersion, and (2) the desired aspect-ratio determined at Block Bin FIG. 3A1. Notably, this step of the design method involves designingthe dual-DOE laser beam modifying subsystem using either of the opticaldesign procedures described in detail hereinbelow,

[0211] As indicated at Block H in FIG. 3A3, the eighth step in thedesign method involves determining the theoretical distance from the VLDto the first lens element L1 that produces an output laser beam havingthe desired beam size determined at Block D. Notably, this computationis carried out assuming a VLD beam having an elliptical spot alignedalong the optical axis of lens L1.

[0212] As indicated at Block I in FIG. 3A3, the ninth step in the designmethod involves determining the focal length of lens element L1 thatproduces an output laser beam having the desired focus determined atBlock C in FIG. 3A1.

[0213] Methods for Designing Laser Beam Producing Systems of theIllustrative System Embodiments of the Present Invention Where FocusControl and Astigmatism Correction are Desired and Delta-Focusing is NotRequired: System Embodiments Nos. (2), (3), (6), (7), (9), & (11)

[0214] System Embodiment Nos. (2), (3), (6), (7), (9) and (11) of thelaser beam producing system of the present invention can be designedusing the below-described design methodology, wherein the steps thereofare set forth in FIGS. 3B1 through 3B2.

[0215] As indicated at Block A in FIG. 3B1, the first step in the designmethod involves establishing end-user requirements for the laser beamproducing module under design. In bar code symbol scanning applications,where the laser beam output from the system under design is to be usedto scan the elements of bar code symbols, such end-user requirement willtypically include, for example, the working distance from the scanningsystem, the depth of field of the scanning system, the type of bar codesymbols that the laser beam must read, the minimal width of the elementsin the bar code symbols, etc.

[0216] As indicated at Block B, the second step in the design methodinvolves determining the necessary spot-size, aspect-ratio and waistdimensions of the output laser beam in order to scan the desired barcode determined during step (1) described in Block A.

[0217] As indicated at Block C, the third step in the design methodinvolves determining the module focal distance, f_(module), that willprovide the desired depth of field for the end-user scanning system.

[0218] As indicated at Block D in FIG. 3B1, the fourth step in thedesign method involves using a Gaussian beam propagation model todetermine the required beam-size and aspect-ratio leaving the laser beamproducing system. Notably, the steps at Blocks B, C and D are somewhatinterconnected inasmuch as the beam spot-size, depth-of-field, and focaldistance are all aspects of Gaussian beam propagation. The values ofeach of these parameters have an effect on the other parameters.Therefore, it is understood that the order in which such parameters aredetermined may be different, from embodiment to embodiment.

[0219] As indicated at Block E in FIG. 3B2, the fifth step in the designmethod involves choosing an acceptable laser source (e.g. a VLD).Criteria for acceptability may include limits on beam divergence andamount of astigmatism, as well as aspect ratio, wavelength, andbandwidth.

[0220] As indicated at Block F in FIG. 3B2, the sixth step in the designmethod involves determining an appropriate value for the beam-shapingfactor of DOEs D1 and D2 which ensures that the aspect-ratio of the beamentering the laser beam-modifying subsystem (D1 and D2) from the VLD issufficiently modified so that output laser beam has the desiredaspect-ratio determined at Block D described above. Notably, thebeam-shaping factor M (also called the expansion ratio), defined asM=M₁M₂, provides beam compression within the laser beam modifyingsubsystem when M<1, and provides beam expansion within the laser beammodifying subsystem when M>1.

[0221] As indicated at Block G in FIG. 3B2, the seventh step in thedesign method involves using the beam-shaping factor determined at BlockF, to determine the design angles, θ_(i1), θ_(d1), θ_(i2) and θ_(d2)(expressed at the reconstruction wavelength, λ_(R)) for the two DOEs D1and D2, which provides an optical subsystem wherein the laser beamoutput from the second DOE D2 thereof has (1) effectively zero net beamdispersion, and (2) the desired aspect-ratio determined at Block B inFIG. 3A1. Notably, this step of the design method involves designing thedual-DOE laser beam modifying subsystem using either of the opticaldesign procedures described in detail hereinbelow.

[0222] As indicated at Block H in FIG. 3B3, the eighth step in thedesign method involves determining the distance from the VLD to thefirst lens element L1 that produces an output laser beam having thedesired beam size determined at Block D. Notably, this calculation iscarried out assuming that the elliptical beam produced from the VLD 4 isaligned along the optical axis of lens L1.

[0223] The remaining design procedure diverges for the presentembodiments ((2), (3), (6), (7), (9) and (11)); therefore, the remainingsteps will be handled below on a by embodiment basis.

[0224] System Embodiment Nos. (2) & (6):

[0225] For System Embodiment Nos. (2) and (6), the ninth step in thedesign method involves determining the focal length of lens L1 so that,when the correct amount of separation exists between the VLD and lensL1, the resulting convergence/divergence of the laser beam willeliminate astigmatism upon passing through both DOEs Di and D2.

[0226] The tenth step in the design method for embodiments (2) and (6)involves determining the focal length of lens L2 in order to focus thebeam at the desired focal point determined at Block C in FIG. 3B1.

[0227] System Embodiment Nos. (3) & (7):

[0228] For System Embodiment Nos. (3) and (7), the ninth step in thedesign method involves determining the focal length of lens L1 so that,when the correct amount of separation exists between the VLD and lensL1, the resulting convergence/divergence of the laser beam willeliminate astigmatism upon passing through DOE D1 only.

[0229] The tenth step in the design method for embodiments (3) and (7)involves determining the design parameters of DOE D2 in order to focusthe beam at the desired focal point determined at Block C in FIG. 3B1.In these embodiments, DOE D2 is a stigmatic element.

[0230] System Embodiment Nos. (9) & (11):

[0231] For System Embodiment Nos. (9) and (11), the ninth step in thedesign method involves determining the focal length of lens L1 so that,when the correct amount of separation exists between the VLD and lensL1, the resulting convergence/divergence of the laser beam will producea predetermined amount of astigmatism upon passing through DOE D1 only.

[0232] The tenth step in the design method for embodiments (9) and (11)involves determining the focal length of lens L2 in order to focus thebeam at the desired focal point determined at Block C in FIG. 3B1. Theknown astigmatic beam entering lens L2 will be focused through DOE D2resulting in a focused, stigmatic spot.

[0233] Methods for Designing Laser Beam Producing Systems of theIllustrative System Embodiments of The Present Invention Where FocusControl, Astigmatism Correction and Delta-Focusing in Output Laser Beamare Desired: System Embodiments Nos. (4), (8), (10) (12)

[0234] System Embodiment Nos. (4), (8), (10) and (12) of the laser beamproducing system hereof can be designed using the below-described designmethodology, wherein the steps thereof are set forth in FIGS. 3C1through 3C.

[0235] As indicated at Block A in FIG. 3C1, the first step in the designmethod involves establishing end-user requirements for the laser beamproducing module under design. In bar code symbol scanning applications,where the laser beam output from the system under design is to be usedto scan the elements of bar code symbols, such end-user requirement willtypically include, for example, the working distance from the scanningsystem, the depth of field of the scanning system, the type of bar codesymbols that the laser beam must read, the minimal width of the elementsin the bar code symbols, etc.

[0236] As indicated at Block B, the second step in the design methodinvolves determining the necessary spot-size, aspect-ratio and waistdimensions of the output laser beam in order to scan the desired barcode determined during step (1) described above.

[0237] As indicated at Block C, the third step in the design methodinvolves determining the module focal distance, f_(module), that willprovide the desired depth of field for the end-user scanning system atthe desired working distance.

[0238] As indicated at Block D in FIG. 3C1, the fourth step in thedesign method involves using a Gaussian beam propagation model todetermine the required beam-size and aspect-ratio leaving the laser beamproducing system. Notably, the steps at Blocks B, C and D are somewhatinterconnected inasmuch as the beam spot-size, depth-of-field, and focaldistance are all aspects of Gaussian beam propagation. The values ofeach of these parameters have an effect on the other parameters.Therefore, it is understood that, from embodiment to embodiment, theorder of determination of such parameters may be different.

[0239] As indicated at Block E in FIG. 3C2, the fifth step in the designmethod involves choosing an acceptable laser source (e.g. a VLD).Criteria for acceptability may include limits on beam divergence andamount of astigmatism, as well as aspect ratio, wavelength, andbandwidth.

[0240] As indicated at Block F in FIG. 3C2, the sixth step in the designmethod involves determining an appropriate value for the beam-shapingfactors of DOEs D1 and D2 which ensures that the aspect-ratio of thebeam entering the laser beam-modifying subsystem (D1 and D2) from theVLD is sufficiently modified so that output laser beam has the desiredaspect-ratio determined at Block D described above. Notably, thebeam-shaping factor M (also called the expansion ratio), defined asM=M₁M₂, provides beam compression within the laser beam modifyingsubsystem when M<1, and provides beam expansion within the laser beammodifying subsystem when M>1.

[0241] As indicated at Block G in FIG. 3C2, the seventh step in thedesign method involves using the Beam Shaping Factor determined at BlockF, to determine the design angles, θ_(i1), θ_(d1), θ_(i2) andθ_(d2),(expressed at the reconstruction wavelength, λ_(R)) for the twoDOEs D1 land D2, which provides an optical subsystem wherein the laserbeam output from the second DOE D2 thereof has (1) effectively zero netbeam dispersion, and (2) the desired aspect-ratio determined at Block Bin FIG. 3A1. Notably, this step of the design method involves designingthe dual-HOE laser beam modifying subsystem using either of the opticaldesign procedures described in detail hereinbelow.

[0242] As indicated at Block H in FIG. 3C3, the eighth step in thedesign method involves determining the distance from the VLD to thefirst lens element L1 that produces an output laser beam having thedesired beam size determined at Block D.

[0243] As indicated in Block I in FIG. 3C2, the ninth step in the designmethod involves determining the focal length of lens L1 so that, whenthe correct amount of separation exists between the VLD and lens L1, theresulting convergence/divergence of the laser beam will eliminateastigmatism upon passing through DOE D1 only.

[0244] As indicated at Block J in FIG. 3C3, the tenth step of the designmethod is to assume DOE D2 to be a stigmatic optical element with nooptical power (it is not, in general, for System Embodiment Nos. 4, 8,10, 12) and then determine the focal length of the final lens element L2in the system such that the desired “average” focal distance of theoutput laser beam is achieved.

[0245] As indicated at Block K in FIG. 3C3, the eleventh step of thedesign method involves determining the design parameters of HOE D2 thatproduce the desired delta-focus of the laser beam through the lens L2.

[0246] Methods for Designing Laser Beam Producing Systems of theIllustrative System Embodiments of the Present Invention WhereAstigmatism Correction is Desired But Neither Focus Control norDelta-Focusing are Required: System Embodiments Nos. (13) & (14)

[0247] System Embodiment Nos. (13) and (14) of the laser beam producingsystem of the present invention can be designed using thebelow-described design methodology, wherein the steps thereof are setforth in FIGS. 3D1 through 3D3.

[0248] As indicated at Block A in FIG. 3D1, the first step in the designmethod involves establishing end-user requirements for the laser beamproducing module under design. These embodiments are similar instructure to System Embodiment Nos. (1) and (5). However, since thedesign goal here is different, the use will be different as will theend-user requirements. For the sake of this discussion, the chosenrequirements will be a set final aspect ratio and beam spot size.Notably for this discussion, the beam-shaping that occurs willnecessarily be aspect-ratio reduction. It is understood that one skilledin the art could adjust this design procedure to meet a differentcombination of end-user requirements.

[0249] As indicated at Block B in FIG. 3D1, the second step in thedesign method involves using a Gaussian beam propagation model todetermine the required beam aspect-ratio leaving the laser beamproducing system in order to produce the specified aspect-ratio atfocus.

[0250] As indicated at Block C in FIG. 3D1, the third step in the designmethod involves choosing an acceptable laser source (e.g. a VLD).Criteria for acceptability may include limits on beam divergence andamount of astigmatism, as well as aspect ratio, wavelength, andbandwidth.

[0251] As indicated at Block D in FIG. 3D1, the fourth step in thedesign method involves determining an appropriate value for thebeam-shaping factors of DOEs D1 and D2 which ensures that theaspect-ratio of the beam entering the laser beam-modifying subsystem (D1and D2) from the VLD is sufficiently modified so that output laser beamhas the desired aspect ratio determined at Block B described above.Notably, the beam-shaping factor M (also called the expansion ratio),defined as M=M₁M₂, provides beam compression within the laser beammodifying subsystem when M<1, and provides beam expansion within thelaser beam modifying subsystem when M>1.

[0252] As indicated at Block E in FIG. 3D2, the fifth step in the designmethod involves using the beam-shaping factor determined at Block D, todetermine the design angles, θ_(i1), θ_(d1), θ_(d2) and θ_(d2)(expressed at the reconstruction wavelength, λ_(R)) for the two DOEs D1and D2, which provides an optical subsystem wherein the laser beamoutput from the second DOE D2 thereof has (1) effectively zero net beamdispersion, and (2) the desired aspect-ratio determined at Block B.Notably, this step of the design method involves designing the dual-DOElaser beam modifying subsystem using either of the optical designprocedures described in detail hereinbelow.

[0253] As indicated at Block F in FIG. 3D2, the sixth step in the designmethod involves determining the convergence of the beam leaving lens L1that will adjust or eliminate the astigmatism produced by the VLD.Specifically for this discussion it is known that the beam willconverge. Once the convergence is known, the focus location, can becalculated.

[0254] As indicated at Block G in FIG. 3D2, the seventh step in thedesign method involves using a Gaussian beam propagation model todetermine the required beam spot size leaving the laser beam producingsystem in order to produce the focused spot size determined at Block A.

[0255] As indicated at Block H in FIG. 3D2, the eighth step in thedesign method involves determining the distance from the VLD to thefirst lens element D1 that produces an output laser beam having thedesired beam size determined at Block G.

[0256] As indicated at Block I in FIG. 3D3, the ninth step in the designmethod involves determining the focal length of lens element D1 thatproduces a beam with the convergence determined in Block F.

[0257] A First Procedure For Determining The Design Angles For TheDiffractive Optical Elements Within The Laser Beam Modifying SubassemblyOf The System Of The Present Invention

[0258] In order to determine the design angles for DOEs D1 and D2 withinthe dual-DOE laser beam modifying subsystems hereof, it is necessary toconstruct a geometric optics model thereof. For the sake ofsimplification, each DOE in each subsystem is represented using a“central-ray” model, as shown in FIG. 3E. Using this reasonable modelingassumption, DOE D1 can be represented as a first fixed spatial-frequencyhologram having fringe-spacing dl, whereas DOE D2 can be represented asa second fixed spatial-frequency hologram having fringe-spacing d2. Thiscentral-ray model provides a perfect description for the central ray ofthe laser beam, in all cases herein considered, but less than a perfectdescription for non-collimated rays (i.e. rays not parallel to thecenter ray of the laser beam). If the beam passing through DOEs D1 andD2 has a relatively large f/#, then the effect of the non-collimatedrays will be negligible.

[0259] In defining the laser beam modifying (optics) subsystem, theangle of incidence of the laser beam from lens L1 onto the front surfaceof first fixed-spatial-frequency DOE (D1) is specified by θ_(i1),whereas the angle of diffraction therefrom is specified by θ_(d1), asillustrated in FIG. 3E. The angle of incidence of the laser beam fromthe first fixed spatial-frequency DOE D1 onto the front surface ofsecond fixed spatial-frequency DOE D2 is specified by θ_(i2), whereasthe angle of diffraction therefrom is specified by θ_(d2). These fourparameters θ_(i1), θ_(d1), θ_(i2), θ_(d2) completely define the dual-DOEsubsystem hereof, and thus provides four degrees of freedom within thegeometrical optics model thereof. Applying the well known “diffractiongrating” equation to the first and second DOEs, D1 and D2, respectively,the following two system equations are obtained: $\begin{matrix}{\frac{\lambda_{R}}{d_{1}} = {\sin^{\theta_{i1}} + \sin^{\theta_{d1}}}} & ( {{Eq}.\quad 1} ) \\{\frac{\lambda_{R}}{d_{2}} = {\sin^{\theta_{i2}} + \sin^{\theta_{d2}}}} & ( {{Eq}.\quad 2} )\end{matrix}$

[0260] wherein the parameter λ_(R) is the design (i.e. reconstruction)wavelength of the laser beam used during reconstruction, and parametersd₁ and d₂ are the surface spacing of the fringes within the first andsecond DOEs D1 and D2, respectively.

[0261] Using simple geometry, the following expression is obtained:

ρ=θ_(d1)−θ_(i2)  (Eq. 3)

[0262] wherein ρ, the DOE tilt angle, is the angle formed between thesurfaces of the two DOEs D1 and D2 within the laser beam modifyingsubsystem under design. Notably, parameter ρ has been previously definedin the geometrical optics model used to design the laser beam productionmodules disclosed in Applicant's copending U.S. patent application Ser.No. 08/573,949 filed Dec. 18, 1995, incorporated herein by reference.

[0263] The above-described geometrical optics model will be used todetermine the optimum configuration of the dual-DOE subsystem whichproduces an output laser beam having minimum beam dispersion andprescribed beam aspect-ratio. Notably, correction for laser beamastigmatism is not addressed in this modeling procedure; however, thisdoes not preclude the ability to control astigmatism when this procedureis used. The dual-DOE subsystem contains four degrees of design freedom,wherein two of those degrees of freedom are removed by requiring minimumdispersion and a specific beam expansion. This leaves two additionaldegrees of freedom in the design process to meet some additional designgoals.

[0264] Specifying the Design Criteria for the Laser Beam ModifyingSubsystem of the Present Invention

[0265] In the illustrative embodiments, the dual-DOE laser beammodifying subsystem must satisfy two design constraints, namely: (1) foran input laser beam having a first specified beam aspect-ratio, producean output laser beam having a second specified beam aspect-ratio; and(2) produce an output laser beam, wherein the dispersion characteristicsor “dispersion” thereof (defined by dθ_(d2)/dλ) are minimized over thespectral bandwidth of the VLD beam.

[0266] The first design constraint is achieved by compressing orexpanding one dimension of the laser beam incident upon the first DOED1. Thus, this design constraint is best described as the laserbeam-shaping factor (e.g. expansion ratio), M, which is equal to theproduct of the individual expansion ratios for DOEs D1 and D2,designated by M₁ and M₂, respectively, wherein M₁=D_(output/D) _(input1)and M₂=D_(output2)/D_(input2) , and D represents dimension of the beamin the compression/expansion direction (i.e. common plane of incidenceof DOEs D1 and D2). In order to meet this design constraint, thefollowing equations must be satisfied: $\begin{matrix}{M_{1} = \frac{\cos \quad \theta_{d1}}{\cos \quad \theta_{i1}}} & ( {{Eq}.\quad 4} ) \\{M_{2} = \frac{\cos \quad \theta_{d2}}{\cos \quad \theta_{i2}}} & ( {{Eq}.\quad 5} )\end{matrix}$

[0267] The second constraint (i.e. relating to minimizing dispersion) isachieved by satisfying the following equation:

d ₂ cos θ_(i2) =d ₁ cos θ_(d1)  (Eq. 6)

[0268] wherein parameters d₁ and d₂ are the surface spacing of thefringes within the first and second DOEs D1 and D2, respectively.

[0269] A First Procedure for Designing the Dual-DOE Subsystem so thatthe Prespecified Design Constraints are Satisfied

[0270] An optimal design for the dual-DOE laser beam modifying subsystemhereof, which satisfies the above-specified design constraints, can bedetermined using the following procedure in conjunction with thegeometrical optics model described above.

[0271] As indicated at Block A in FIG. 3F1, the first step of the designprocedure involves choosing values for the beam compression/expansionratios M₁ and M₂ such that the total desired Beam Shaping Factor Msatisfies the expression M=M₁M₂. Also, at this stage of the designmethod, the design (i.e. reconstruction) wavelength λ_(R), and the angleof incidence θ_(i1), are chosen by the DOE-subsystem designer.

[0272] As indicated at Block B in FIG. 3F1, the second step of thedesign procedure involves solving for the angle of diffraction θ_(d1) atDOE D1 using Equation No. (4) set forth above.

[0273] As indicated at Block C in FIG. 3F1, the third step of the designprocedure involves solving for the fringe structure (surface) spacingd₁, of DOE D1, using Equation No. (1) set forth above.

[0274] As indicated at Block D in FIG. 3F1, the fourth step of thedesign procedure involves solving for the angle of incidence θ_(i2) atDOE D2, using the following equation: $\begin{matrix}{\theta_{i2} = {{{\arctan \lbrack {{\frac{1}{2}\underset{\underset{\underset{\overset{\sim}{a}}{\overset{¨}{a}}}{e}}{\overset{¨}{a}}M_{2}^{2}K} - K + {\frac{1}{K}\underset{\underset{\overset{\prime}{i}}{\overset{\prime}{i}}}{\overset{¨}{e}}}} \rbrack}\quad {where}\quad K} = \frac{d_{1}\cos \quad \theta_{d1}}{\lambda}}} & ( {{Eq}.\quad 7} )\end{matrix}$

[0275] As indicated at Block E in FIG. 3F1, the fifth step of the designprocedure involves solving for the DOE tilt angle ρ, using Equation No.(3).

[0276] As indicated at Block F in FIG. 3F2, the sixth step of the designprocedure involves solving for the angle of diffraction θ_(d2) at DOED2, using Equation No. (5).

[0277] As indicated at Block G in FIG. 3F2, the seventh step of thedesign procedure involves solving for the fringe surface spacing d₂within DOE D2, using Equation No. (2).

[0278] The above described parameters specify the design parameters forthe dual-DOE subsystem at the reconstruction wavelength λ_(R) whichtypically be specified by the characteristic wavelength of the VLD usedto realize the laser beam producing system under design.

[0279] A Second Procedure for Determining the Design Angles for theDiffractive Optical Elements Within the Laser Beam Modifying Subassemblyof the System of the Present Invention

[0280] According to the second design procedure, the two equations for(1) zero beam dispersion and (2) the desired beam aspect-ratio aresolved and then graphed (i.e. plotted) to determine the intersection ofthe two functions which yields the design point at which both designrequirements are simultaneously satisfied. Typically, a few iterationsof the solutions of the equations will be required to determine thedesign point to an acceptable level of precision. This procedure hasbeen described in detail in Applicant's copending application Ser. No08/573,949, incorporated herein by reference.

[0281] Notably, the graphical approach described hereinabove providesadditional information about the residual dispersion that will existwhen the wavelength of the VLD laser beam differs from the designwavelength. The graphical approach also provides information regardingthe rate of change of dispersion as a function of laser beam wavelength,which is useful in particular applications. Such information can also beobtained from the model employed in the First Procedure described aboveusing Equation (8) which will be described in greater detailhereinafter.

[0282] Considerations When Designing The DOE-Based Subsystem of ThePresent Invention

[0283] When designing a DOE-based laser beam modifying subsystem hereofusing either of the design procedures set forth above, the followingfactors should be considered.

[0284] First, it is desirable to select angles of incidence anddiffraction that are not too large or too different in magnitude. Thiswill make the construction of the DOEs simpler. This is an example of asupplementary goal that can be met by exercising the aforementionedunused degrees of freedom in the laser beam modifying subsystem design.Second, it is desirable to have the angular separation between theincident beam at DOE D1 and the diffracted beam at DOE D2 greater thanzero so as to avoid interference between the zero-order beam from DOE D1and the diffracted beam from DOE D2. As this may be difficult to do, itmay be necessary to provide a blocking plate or surface between the twoDOEs as shown in illustrative embodiments of the present invention inFIGS. 6C, 10C. and 11C. Notably, in such illustrative embodiments, theblocking plate is provided as an integral part of the module housing.

[0285] Considerations on Aspect-Ratio Control and Beam DispersionMinimization/Elimination

[0286] Provided that the desired parameters are reasonable, the systemand assembly methods of the present invention enable the construction ofoptical systems capable of producing output laser beams having (1) adesired beam aspect-ratio and (2) zero or minimum beam dispersion. Thesedesign objectives can be accomplished over a fairly wide range of beamaspect-ratios, angles of incidence and diffraction, and angles betweenthe two DOES. For all of the system embodiments herein, beam dispersioncorrection is perfect only for the center ray in the system. However, ifthe angle of the cone of rays passing through the laser beam modifyingsubsystem is relatively small, then beam dispersion correction, whilenot perfect, will be acceptable in many applications. In bar codescanning applications where, for example, the f-number of the focusingcone of light rays is generally on the order of 200 or more (so that thefull angle subtended by the cone of light rays (i.e. the full coneangle) is less than 0.3 degrees), beam dispersion correction will bemore than adequate for all rays within the light cone incident on theDOEs D1 and D2.

[0287] Considerations on Astigmatism Correction

[0288] When proceeding to eliminate astigmatism in the output laser beamfrom the laser beam producing module, the resulting pair of designedDOEs does not change in any way. In accordance with the principles ofthe present invention, astigmatism correction is accomplished byadjusting the separation between the VLD and the first lens L1 duringthe alignment stage of the system assembly process of the presentinvention. The amount of adjustment is dependent on the fixed parametersof the DOE pair (e.g. diffraction angles and angle between DOEs D1 andD2) and the beam characteristics of each VLD used in the construction ofeach laser beam producing system.

[0289] Notably, it is possible to specifically design the laser beammodifying subsystem to eliminate a specific amount of astigmatism for agiven desired focus as accomplished, for example, in System EmbodimentNos. (13) and (14). When designing such systems, the beam-shapingfactor, M, can be specifically chosen to eliminate astigmatism. In allof the other system embodiments disclosed herein the beam shaping factorM is used to control aspect-ratio. However, when designing a system toeliminate astigmatism, it is understood that aspect-ratio control willbe sacrificed in order to reduce astigmatism. The specific systemembodiments disclosed herein can be modified using such teachings toprovide numerous other types of system designs in accordance with theprinciple of the present invention.

[0290] The inherent astigmatism of the laser beam produced from the VLDis modified or eliminated by adjusting the convergence or divergence ofthe beam incident on the dual-DOE laser beam-modifying subsystem hereof.If the laser beam-modifying subsystem is used to expand the narrowerdimension of the VLD beam or to compress the wider dimension of the VLDbeam (i.e. aspect-ratio reduction), then the astigmatism is minimized byusing a converging beam incident on the laser beam-modifying subsystem.If the laser beam-modifying subsystem is used to compress the narrowerdimension of the VLD beam or to expand the wider dimension of the VLDbeam (i.e. aspect-ratio enlargement), then the astigmatism is minimizedby using a diverging beam incident on the laser beam-modifyingsubsystem.

[0291] Considerations on Adjustment of the Focal Length of the StigmaticOutput Laser Beam

[0292] Relatively simple optics following the laser beam-modifyingsubsystem, as shown in FIG. 2H, 2J, and 2L, can be used to focus theastigmatism-free (stigmatic) beam produced by the subsystem. By placinga second lens L2 after the variable spatial-frequency DOE D2, as inSystem Embodiment Nos. 4 and 8, or before the variable spatial-frequencyDOE D2, as in System Embodiments Nos. 10 and 12, the laser beamproducing system is provided with a means for adjusting (i.e.fine-tuning) the focal length the stigmatic output laser beam. Thisfeature is advantageous in applications where, for example, the laserbeam producing system functions as an optical subsystem within a largeroptical system, and the laser beam output therefrom is to be furthermodified in terms of focal length and the like.

[0293] Analyzing the Dispersion Associated with the Laser Beam Outputfrom the Laser Beam

[0294] Producing System Designed in Accordance with the Principles ofthe Present Invention Having designed a laser beam producing systemusing the above-described design procedure, the dispersioncharacteristics thereof can be analyzed by using the following equation:$\begin{matrix}{{\theta_{d2}\overset{\prime}{a}\lambda_{R}\overset{\prime}{e}} = {\arcsin\lbrack {\frac{\lambda_{R}}{d_{2}} + {\sin \quad \rho \sqrt{1 - {\underset{\underset{\underset{\overset{\sim}{a}}{\begin{matrix}a \\a\end{matrix}}}{a}}{\overset{¨}{a}}\frac{\lambda_{R}}{d_{1}}} - {\sin \quad \theta_{i1}\underset{\begin{matrix}i \\i \\i \\\overset{\prime}{i}\end{matrix}}{{\overset{¨}{e}}^{2}}}}} - {\cos \quad \rho \underset{\underset{\underset{\overset{\sim}{a}}{\begin{matrix}a \\a\end{matrix}}}{a}}{\overset{¨}{a}}\frac{\lambda_{R}}{d_{1}}} - {\sin \quad \theta_{i1}\underset{\begin{matrix}i \\i \\i \\\overset{\prime}{i}\end{matrix}}{\overset{¨}{e}}}} \rbrack}} & ( {{Eq}.\quad 8} )\end{matrix}$

[0295] Equation (8) can be used to plot the deflection (i.e.diffraction) angle of each wavelength component in the laser beam outputfrom any laser beam producing system designed and constructed inaccordance with the principles of the present invention. A geometricaloptics model is presented in FIG. 5A for dispersion analysis of theoutput laser beam. A graphical representation of dispersion analysis isprovided in FIG. 5B, showing a plot of diffraction angle θ_(d2) as afunction of wavelength component of the output laser beam. Inasmuch asthe sole objectives for the DOE-subsystem design process describedhereinabove are shaping the laser beam without introducing dispersion,the values for the expansion factors M₁ and M₂ and angle of incidenceOil specified at Block A in FIG. 3E1 can be varied to obtain virtuallyany acceptable solution (provided that the Beam Shaping Factor M=M₁M₂ issatisfied).

[0296] Using the Beam Dispersion Equation (Eq. 8) set forth above, onecan predict the behavior of the laser beam producing system, as well asdesign a system that will perform in the manner required by anyparticular application at hand.

[0297] Unlike conventional optical elements, the dispersion of theDOE-based laser beam-modifying subsystem can be adjusted so that thefunction θ_(d2) (X) exhibits a minimum or a maximum value reflected in agraphical representation thereof. The maximum or minimum point is theprecise design point of zero dispersion. If desired or required by anyparticular application, the dispersion characteristics can be modifiedin a variety of ways.

[0298] For example, if the DOE-based subsystem hereof is used tocompress the laser beam produced from the subsystem comprising the VLDand lens L1, as in the illustrative embodiments shown in FIGS. 2A, 2B,2C, 2D, 2I, 2J, and 2M, then the minimum dispersion curve for the laserbeam output from the resulting laser beam producing system will have anegative curvature (i.e. its graphical representation is concavedownward), as illustrated in FIGS. 5 and 5B1. If the DOE-based systemhereof is used to expand the laser beam produced from the subsystemcomprising the VLD and lens L1, as in the illustrative embodiments shownin FIGS. 2E, 2F, 2G, 2H, 2K, 2L, and 2N, then the minimum dispersioncurve for the laser beam output from the resulting laser beam producingsystem will have a positive curvature (i.e. its graphical representationis concave upward), as illustrated in FIGS. 5 and 5B2.

[0299] If DOE-based subsystem hereof neither expands nor compresses theinput laser beam (i.e. the Beam Shaping Factor M of the subsystem isunity), then the dispersion curve for the output laser beam will beperfectly flat, as illustrated in FIG. 5B. This unique case occurs onlywhen the two DOEs D1 and D2 of the subsystem are arranged parallel toeach other and the laser beam entering the DOE D1 is parallel to thebeam leaving the DOE D2.

[0300] Various Options Available For Implementing the DOE-Based LaserBeam Modifying Subsystem of the Present Invention

[0301] In general, there are a variety of different techniques availablefor implementing (i.e. realizing) the DOEs of the DOE-based subsystem 2described in great detail hereinabove. One technique known in the artwould involve the use of conventional “optically-based” holographicrecording techniques, wherein each designed DOE of the subsystem isrealized as a volume transmission hologram (HOE) constructed by theinterference of a laser “object” beam and a laser “reference” beamwithin a photosensitive recording medium. Another technique known in theart would involve the use of computer generated holographic techniques,wherein each designed DOE of the subsystem is realized as a copy ofcomputer-generated hologram (CGH) by computer modelling the interferencepattern and producing the same through printing techniques to produce ahologram having performance characteristics specified during the designprocess. Other techniques, while less preferred, could involve the useof micro-etching of optical structures to produce “surface-reliefholograms” having performance characteristics specified during thedesign process of the present invention. For purposes of illustration,techniques for producing HOE, CGH and surface-relief implementations ofthe DOE-based subsystem hereof will be described in greater detailhereinbelow.

[0302] Implementing The DOE-based Subsystem Using Optical-BasedHolographic Recording Techniques: Two Cases To Consider

[0303] Prior to teaching particular procedures for making fixed spatialfrequency and variable spatial frequency HOEs, it will be helpful toprovide a brief overview on these different holographic constructiontechniques.

[0304] Case 1: Constructing Fixed Frequency HOEs

[0305] When constructing a fixed frequency hologram (HOE), the objectand reference beams must have the same radius of curvature. In mostapplications, this is accomplished by collimating the two beams so thatwe have two wavefronts at the hologram recording medium. The anglebetween the two beams will determine the spatial frequency of the fixedfrequency hologram. The greater the angle, the greater the spatialfrequency. The actual spatial frequency of the hologram is, moreprecisely, a function of the angles of incidence of the two beams at thehologram recording medium and the wavelength of the two beams. Thespatial frequency is established by the well known grating equation:d=wavelength/(sinO+sinR), where O is the angle of incidence of theobject beam and R is the angle of incidence of the reference beam.

[0306] Case II: Constructing Variable Frequency HOEs

[0307] When constructing a variable frequency hologram (HOE), the objectand reference beams must have different radii of curvature. In mostapplications, this is accomplished by collimating one of the beams andmaking the other beam a diverging beam. We will choose to call thecollimated beam the reference beam. The diverging beam, which we willchoose to call the object beam, is generally created by transmitting theobject beam portion of the laser beam through a positive lens, such as amicroscope objective. The focal point of the converging beam leaving thepositive lens then becomes the center of curvature of the object beam.If this positive lens is a spherical lens, the object beam wavefront atthe hologram recording medium will be spherical. If the lens iscylindrical lens, with optical power in only one dimension, the objectbeam wavefront at the hologram recording medium will be cylindrical. Inthe case of cylindrical wavefront, some additional spherical optics isgenerally employed to expand the cylindrical beam along the axis of thecylinder without modifying the wavefront in that direction. That is, inthe direction parallel to the cylindrical axis of the wavefront the beamwill appear to be collimated.

[0308] As in the fixed frequency hologram, the wavelength of the beamsand the angles of incidence of the two beams at the hologram recordingmedium will determine the spatial frequency of the hologram. However, inthis case, the angle of incidence of the object is not constant sincethe beam has spherical (or cylindrical) wavefront. The angle ofincidence of any beam at the point of incidence of any surface is theangle between the normal to the surface and the incoming ray at thepoint of incidence. And the incoming ray, by definition, is just thenormal to the wavefront. But for a spherical, or cylindrical, wavefront,the normal to the wavefront will not be constant across the wavefront.The angle of incidence for the object beam will be the angle between thenormal to the surface and the line running from the point of incidenceto the center of curvature of the object beam. Since this angle willvary with position on the hologram recording medium, then, from thegrating equation, the spatial frequency will also vary with position onthe hologram recording medium. That is, we will have a variablefrequency hologram.

[0309] The spatial frequency of this variable frequency hologram willvary in both (x and y) dimensions of the plane of the hologram recordingmedium when the object beam is a spherical wavefront. The spatialfrequency of this variable frequency hologram will vary in only onedimension of the plane of the hologram recording medium when the objectbeam is a cylindrical wavefront.

[0310] Having provided an overview on these different constructiontechniques, it is now appropriate to disclose hereinbelow preferredprocedure of constructing both fixed and variable spatial frequencyHOEs.

[0311] A Procedure for Constructing Fixed and Variable Spatial FrequencyHOEs

[0312] As indicated at Block A in FIG. 4A, the design parameters θ_(i1),θ_(d1), θ_(i2), θ_(d2) and f₂ (i.e. focal length of DOE D2 in the caseof variable spatial frequency DOES) expressed at the reconstructionwavelength λ_(R) are converted into construction parameters expressed atthe construction wavelength λ_(C) namely: object and reference beamangles θ_(O1) and θ_(R1) for HOE H1 at construction wavelength λ_(C);and object and reference beam angles θ_(O2) and θ_(R2), respectively,for HOE H2. This parameter convention process can be carried out using,for example, the conversion method described on Pages 163-164 and FIGS.28A1 through 28D and FIG. 29 of International Publication No.WO/9722945, based on corresponding U.S. application Ser. Nos. 08/573,949and 08/726,522, each of which is incorporated herein by reference.Notably, instances where the design (reconstruction) wavelength λ_(R) isequal to the construction wavelength λ_(C) and there is no need forwavelength correction or conversion, then the design parameters can beused for the construction parameters in a manner well known in the art.

[0313] As indicated at Block B in FIG. 4A, it will be necessary, in thecase of variable spatial frequency DOEs, to use computer ray-tracinganalysis in order to determine the distances of the object and referencesources relative to the recording medium (as well as the distances ofany aberration-correcting lenses therefrom) which are employed duringthe holographic recording process, schematically depicted in FIG. 4B forthe case of a variable spatial frequency HOE. In the case of fixedspatial frequency DOEs, computer ray-tracing analysis is not necessary.Notably, in this case, the location of the object and reference sourcesrelative to the recording medium will be effectively located atinfinitely (e.g. realized by the use of collimating mirrors or thelike).

[0314] Having computed the construction parameters for HOE H1 and HOEH2, the HOEs can then be constructed using the holographic recordingsystem illustrated in FIG. 4B, using the volume holographic recordingtechniques detailed in International Publication No. WO/9722945, supra.Regarding, non-VLD type astigmatism, the method used to construct HOE H1should seek to minimize the astigmatism that would normally occur when awidely diverging beam is incident on a glass plate with parallelsurfaces. This type of astigmatism can be minimized in many instancesif, for example, the HOE is constructed using: (1) the same type oflaser as is used in the end-user scanning system; and (2) the sameillumination geometry as is used in the end-user scanning system. Whileapplying the above conditions is helpful in many instances, it isunderstood that it is not always necessary, nor is it always possible todo so.

[0315] Implementing The DOE-based Subsystem Using Computer-GeneratedHolographic (CGH) Recording Techniques

[0316] The values obtained for design parameters θ_(i1), θ_(d1), θ_(i2),θ_(d2), d₁, d₂ and f₂ (focal length of variable frequency DOE)associated with the dual-DOE subsystem can be used to deriveconstruction parameters necessary to construct a dual-CGH implementationthereof. A suitable procedure for this type of implementation will bedescribed below.

[0317] As indicated at Block A in FIG. 4C1, the first step of the methodinvolves formulating, within a digital computer system 170, amathematical description of the object and reference beam wavefronts atthe design wavelength Typically, standard diffraction integrals, such asthe Kirchhoff integral, can be used to produce mathematical descriptionsof these wavefronts. Such mathematical descriptions can be derived fromthe design parameters {e.g., for DOE D1, such parameters include θ_(i1),θ_(d1), θ_(i2), θ_(d2), the image produced by DOE D1 (i.e. referencesource point) and image produced from DOE D2 (i.e. object sourcepoint)}. In particular, a mathematical description for the object andreference beam wavefronts at the design wavelengths λ_(R) for DOE D1 canbe formulated as Kirchhoff integrals using the design parameters for DOED1, expressed at the reconstruction (i.e. design) wavelength Also, amathematical description for the object and reference beam wavefronts atthe design wavelength for DOE D2 can be formulated as Kirchhoffintegrals using the design parameters for DOE D2, expressed at thereconstruction wavelength λ_(R). Notably, using the CGH implementationtechnique, there typically will be no need to make any corrections forthe construction wavelength as the CGH has been previously constructedfor aberration-free performance at the reconstruction wavelength (whichis specified by the commercial-grade VLD selected for use inconstructing the laser beam producing system).

[0318] As indicated at Block B in FIG. 4C1, the second step of themethod involves using the digital computer system 170 to formulate amathematical description of the “interference pattern” that is generatedby mathematically superimposing the mathematical model of the objectbeam wavefront (e.g represented by Kirchoff integrals) with themathematical model of the reference beam wavefront (also represented byKirchoff integrals). The mathematical description of the interferencepattern generated by the computer system 170 provides a “spatialfunction” of the interference pattern. In cases where only fixed-spatialfrequency DOEs are used to construct the laser beam modifying subsystem,the interference pattern generated by the reference and objectwavefronts will be mathematically represented by a one-dimensionalsinusoidal function, expressed in the form of D=A+Bsinfx, where A is abias level; B is a modulation factor always less than A; and f is thespatial frequency. In cases where a variable spatial frequency DOE isused to construct the laser beam modifying subsystem, the interferencepattern generated by the reference and object wavefronts can bemathematically represented by an infinite series of one-dimensionalsinusoidal functions.

[0319] As indicated at Block C in FIG. 4C1, the third step of the methodinvolves using the digital computer system 170 to sample the spatialfunction of the computer generated/represented interference patternalong the x and y directions in order to produce a large set of sampledvalues of varying light transmission associated with the computergenerated interference pattern (represented within the computer system170). These sampled values correspond to either the light transmittanceof the computer generated/represented interference pattern over its x,yspatial extent.

[0320] As indicated at Block D in FIG. 4C2, the fourth step of themethod involves transferring the sampled light transmittance values fromthe computer system 170 to the drivers of a graphical plotter orplotting tool 171 shown in FIG. 4C2.

[0321] As indicated at Block E in FIG. 4C2, the plotting system 171 usesthe set of sampled amplitude transmittance values to plot thetwo-dimensional sampled interference pattern on paper or other recordingmedium 172, thereby creating a graphical representation thereof 173consisting of fine (sampled) dots of particular density, in a waysimilar to that produced by a digital printing process. In general, thetwo-dimensional amplitude transmittance function 173 plotted on paper orother recording medium 172 by the plotting tool 171 is usually quitelarge (i.e. several orders larger than the final CGH master). Thetwo-dimensional plot produced from this step of the method provides agraphical representation of the CGH under construction. For fixedspatial frequency DOEs, the 2-D plot provides a graphical representationof a CGH which functions as a planar diffraction grating. For variablespatial frequency DOEs, the 2-D plot provides a graphical representationof a CGH which functions with some degree of focal power.

[0322] As indicated at Block F in FIG. 4C2, two-dimensional amplitudetransmittance function 173 plotted on paper at Block E can then bephotographically reduced on some light transmissive or reflectiverecording medium, generally photographic film 175 using photographicreduction equipment 174. The output of this system is a master of theCGH which can be then bleached to improve its diffraction efficiency.However, its diffraction efficiency will always be low because the CGHis a surface relief hologram, not a volume hologram as produced by theoptically-based Holographic Recording Method described above. As normalphotographic film will often be the medium used for the first recordingof the CGH (at Block F), it is expected that resolution of the CGH willnot be very high.

[0323] As required by most embodiments of the DOE-based subsystemhereof, the CGH master obtained at Block F can be copied onto somehigher efficiency medium, such as DCG, photoresist, or suitable surfacerelief material 177 using conventional copying apparatus 176 well knownin the art. While such copying techniques enable the production of DOEshaving greater diffraction efficiencies, these techniques are notwithout their problems, as explained below.

[0324] For example, copies of a CGH master can be made with highdiffraction efficiency in surface relief material by standard pressingoperations provided that the aspect ratio of the surface reliefstructure (groove depth/groove spacing) is on the order of one. However,it is very difficult to make such copies when the aspect ratio of thesurface relief structure is that large.

[0325] Using photoresist CGH copies directly is also difficult becausethe material is susceptible to damage during handling. Also, sealing thephotoresist CGH copies between glass will be required in manyapplications. However, this will drastically reduce the diffractionefficiency of the photoresist CGH copies if an index matching fluid isused to minimize reflection losses.

[0326] Making DCG copies of the CGH masters at the 488 nm Argonwavelength is a much better method, as the “nearly-contact” copy processwill always faithfully reproduce the surface fringe structure of themaster, regardless of the wavelength of the copying laser light source.Consequently, the copy holograms will be aberration-free at thewavelength at which the CGH masters were constructed (for use withconventional VLDs). The CGH HOEs will be essentially the same as thephotographic plate masters.

[0327] Notably, however, the CGH fabrication technique described abovewill have little advantage over the optically-based HolographicRecording Method. In fact, this technique will have the significantdisadvantage of producing holograms having a much lower resolution. Intypical applications, the DOEs will require a resolution of at least2000 cycles per mm. While the DCG copying method is capable of producingHOE having a resolution better than 2000 cycles per mm, the resolutionof the DCG copy can be no greater than that of the CGH master, which,for normal photographic film, will be much less than 2000 cycles per mm.Consequently, when using the CGH implementation technique describedhereinabove, it will be desirable (if not necessary) to first record theCGH master in a photographic medium having a very high resolution inorder to produce CGH masters having diffraction efficiencies suitablefor use in the DOE-based subsystem hereof.

[0328] Having produced a master CGH in the manner described above,copies thereof can be made using various copying techniques known in theart.

[0329] If the illuminating beam transmitted through the CGH copy (duringreconstruction) is identical to the reference beam (modelled at BlockA), then the object beam (modelled at Block A) will be reconstructed bythe interference pattern embodied within the CGH copy. If theilluminating beam transmitted through the CGH copy (duringreconstruction) is identical to the object beam (modelled at Block A),then the reference beam (modelled at Block A) will be reconstructed bythe interference pattern embodied within the CGH copy.

[0330] Additional details regarding CGH implementation process can foundwith reference to: Chapter 19 of the book entitled “Optical Holography”by Collier, Burckhardt and Lin (1971), published by Academic Press,incorporated herein by reference.

[0331] Applications Of The Laser Beam Producing System Of The PresentInvention

[0332] In general, each illustrative embodiment of the laser beamproducing system described above can be realized in a variety ofdifferent ways. For example, in FIGS. 6A through 10D, several laser beamproduction modules of the present invention are disclosed for producinga laser beam having a pre-specified beam aspect-ratio, zero beamdispersion and a predetermined focus. In FIGS. 11A through 11C, a laserbeam production module of the present invention is shown for producing alaser beam, wherein a pre-specified beam aspect-ratio is achieved, itsbeam dispersion is zero (or minimized), its focus set to a predetermineddistance, and its astigmatism corrected. In FIGS. 12A through 112C, alaser beam production module of the present invention is shown forproducing a laser beam wherein its aspect-ratio is controlled, its beamdispersion is zero (or minimized), its astigmatism corrected, its focusset to a predetermined distance, and its focal length adjusted. Withreference to modified system designs shown in FIGS. 7A through 7C,several laser beam production modules of the present invention aredisclosed for producing a laser beam having a pre-specified beamaspect-ratio, zero beam dispersion and astigmatism control. For purposesof illustration, HOE-based implementations of these illustrative systemembodiments will be described hereinbelow. Equivalent CGH-basedimplementations thereof can be readily made using the principlesdisclosed hereinabove.

[0333] Laser Beam Production Module Of The First Illustrative SystemEmbodiment For Producing A Stigmatic Laser Beam Having Zero BeamDispersion, Predetermined Aspect Ratio and Preset Focus (CASE D)

[0334] In FIGS. 6A, 6B and 6C, a first illustrative embodiment of thelaser beam production system of FIGS. 2M and 2N (System Embodiment Nos.13 and 14) is disclosed. As shown, this optical system is realized inthe form of a miniature laser beam producing module 10 comprising anassembly of subcomponents, namely: a module housing 11 made oflightweight plastic and serving as an optics bench for the opticalcomponents within the laser beam producing system; a VLD 12, press-fitmounted through a metal heat sinking plate 26; a VLD, mounting bracket(i.e. Yoke) 13, having side projecting 13A and 13B slidable withinspaced apart recesses 11A and 11B respectively formed in the rearportion of the module housing: connected to the terminal 14 of the VLD,for applying a supply voltage and driving the VLD to produce a laserbeam having elliptical, divergent, eccentric, and astigmaticcharacteristics, and a oversized aperture 27 for receiving the caseportion (or beam emitting) portion of the VLD and allowing x, ypositioning thereof relative to the VLD mounting bracket 13; a flexiblecircuit 15; a focusing lens L1 16 for focusing the laser beam producedfrom the VLD; fixed spatial-frequency HOE H1 17, securely mounted withina first mounting slot 18 formed in the module housing II, for modifyingthe beam characteristics of the laser beam output from focusing lens L116; fixed spatial-frequency HOE H2 19, securely mounted within a secondmounting slot 20 formed in the module housing 11, for modifying the beamcharacteristics of the laser beam produced from HOE H1 to produce theoutput laser beam; a beam folding mirror 21, mounted on side wallsurface 22 of the module housing, for directing the output laser beamthrough the beam output window 23 formed in the side wall of the modulehousing; a first radiation-absorbing wall surface 24 formed in themodule housing, aligned with the zeroeth-order diffraction beam from HOEH1, and absorbing the zeroeth-order diffraction beam produced from HOEH1; and second radiation-absorbing wall surface 25 formed in the modulehousing, aligned with the zeroth-order diffraction beam from HOE H2, andabsorbing the zeroeth-order diffraction beam produced from HOE H2.

[0335] In an illustrative embodiment of this system design, the VLD 12can be realized using a SONY Model SLD1122VS laser diode, and thefocusing lens L1 16 can be realized as a 4.35 mm lens made of anoptically transparent plastic. The HOEs H1 17 and H2 19 can be madeusing DCG recording material of about 5 microns thick, a constructionwavelength of 488 nanometers. These volume transmission holograms can bemounted between a pair of ultra-small plates made from float glass. Itis understood, however, that other embodiments of this system design canbe made using different types of components and materials, havingdifferent design parameters selected or determined for the particularapplication at hand.

[0336] As shown in FIG. 6C, during the alignment stage of the assemblyprocess for the laser beam producing module 10, the distance between VLD12 and lens L1 16 is adjusted by sliding the VLD mounting bracket 13within the pair of recesses 11A and 11B. As will be explained in greaterdetail hereinafter, this parameter adjustment mechanism is employedwhile the system is mounted on a special design fixture specificallycrafted for aligning such parameters. When the x, y position of the VLDis properly aligned relative to lens L1, by a translation of theVLD/heat-sinking plate subassembly relative to VLD mounting bracket 13during the alignment stage of the module assembly process, then theoutput laser beam from the module will have the desired beamaspect-ratio and minimized (or zero) beam dispersion minimized inaccordance with the design criteria for this laser beam producingmodule. Also, the (z) axis position of the VLD is relative to lens L1can be adjusted during the alignment stage by sliding VLD mountingbracket 13 within recesses 11A and 11B in the module housing until beamastigmatism is eliminated. This parameter alignment process will bedescribed in greater detail hereinafter.

[0337] Laser Beam Producing Module of The Second Illustrative SystemEmbodiment For Producing A Laser Beam Having Focus Control, ControlledAspect-Ratio And Zero Beam Dispersion: CASE A

[0338] In FIGS. 7A, 7B and 7C, a second illustrative embodiment of thelaser beam production System Embodiment No. 1) of FIG. 2M is disclosed.As shown, this optical system is realized in the form of a miniaturelaser beam producing module 30 comprising an assembly of subcomponents,namely: a module housing 31 made of lightweight plastic and serving asan optical bench for the optical components within the laser beamproducing system; a VLD 32 mounted to a VLD heat-sinking plate 33through aperture 33A and producing a visible laser beam havingelliptical, divergent and astigmatic beam characteristics in response toa voltage source applied VLD terminal 34 by way of a flexible circuiterlike connectors (not shown) well known in the art; a mounting bracket 36having an aperture 36A for receiving the barrel portion of the casing ofthe VLD 32 and a mounting surface 36B for affixing the associatedheat-sinking plate 33 and premounted VLD 32 thereto, and also havingside projections 36C and 36D for slidable receipt within spaced apartrecesses 37C and 37D formed in the rear portion of the module housing; acollimating lens L1 38 for focusing the laser beam produced from theVLD; fixed spatial-frequency HOE H1 39, securely mounted within a firstmounting slot 40 formed in the module housing 31, for modifying the beamcharacteristics of the laser beam output from focusing lens L1 38; fixedspatial-frequency HOE H2 41, securely mounted within a second mountingslot 42 formed in the module housing 31, for modifying the beamcharacteristics of the laser beam produced from HOE H1 to produce theoutput laser beam; a radiation-absorbing wall surface 43 formed in themodule housing, aligned with the zeroeth-order diffraction beam from HOEH1, and absorbing the same during operation of the device; and a housingcover plate 44 for attachment to the top portion of the module housing31 and securing HOEs H1 and H2 therein.

[0339] In the illustrative embodiment, the VLD 32 can be realized usinga SONY Model SLD1122VS laser diode, and the collimating lens L1 38 canbe realized as a 4.35 mm lens made of an optically transparent plastic.The HOEs H1 39 and H2 41 can be made using DCG recording material ofabout 5 microns thickness, at a construction wavelength of 488nanometers. These volume transmissions holograms can be mounted betweena pair of ultra-small plates made from float glass. It is understood,however, that other embodiments of this system design can be made usingdifferent types of components and materials, having different designparameters selected or determined for the particular application athand.

[0340] When the proper x, y position of the VLD 32 relative to theoptical axis of lens L1 38 is set during the alignment stage of themodule assembly process, then the output laser beam from the module willhave the desired beam aspect-ratio and minimized (or zero) beamdispersion in accordance with the design criteria for this laser beamproducing module. As shown in FIG. 7C, during assembly and constructionof the laser beam producing module 30, the distance between VLD 32 andlens L1 38 (i.e. “d”) is adjusted by sliding the VLD mounting bracket 36within the pair of recesses 37C and 37D in the module housing. As willbe explained in greater detail hereinafter, this parameter adjustmentmechanism is employed while the system is mounted on an optical benchspecially crafted for aligning such parameters.

[0341] Laser Beam Scanning Module Adapted For Use With The Laser BeamProducing Modules Of The Present Invention

[0342] In FIGS. 8A and 8B, a laser beam scanning module is disclosed foruse with any of the laser beam producing modules of the presentinvention. As shown, the laser beam scanning module 50 comprising anassembly of subcomponents, namely: a module housing 51 made oflightweight plastic and serving as an optical bench for the opticalcomponents within the laser beam scanning system; an electromagneticcoil 52 mounted within recess 53 in the module housing, for producing amagnetic force field FM in response to electrical current supplied tothe input terminals thereof 52A; a scanning element 54 supporting alight deflecting element (e.g. mirror, hologram, refractive element,etc.) 55 on the front surface of its free end, and a permanent magneticelement 56 on the rear surface of its free end; a pair of mountingplates 57 and 58 having projections 57A, 57B, and matching holes 58A,58B respectively for clamping the base portion 54A of the scanningelement 54, and securely mounting the same within recess 59 formedwithin the module housing 51, as shown in FIG. 8B and 9; and a housingcover plate 60 for attachment to the top surface 61 of the modulehousing 51, and securing the scanning mechanism components therewithin,while forming a scanning window 62 through which a laser beam producedfrom a laser beam producing module hereof can pass to the scanningelement and be deflected therefrom out through the scanning windowacross the scan field of the resulting scanning system. Detailsregarding the design and construction of the scanning mechanism formedby the electromagnet 52, the scanning element 54 and the scanningelement anchoring mechanism (formed by plates 57 and 58, and recess 56)are disclosed in copending application Ser. No. 08/931,694 filed Sep.16, 1997, and incorporated herein by reference in its entirety. It isunderstood, however, that there are other scanning mechanisms that maybe embodied within the module housing 51 described above, for use inconjunction with the laser beam producing modules of the presentinvention.

[0343] As shown in FIG. 8A, when scanning element mounting plates 57 and58 are inserted within the mounting recess 59 in the module housing, thetop projections 57C and 58C thereof protrude slightly above the topsurface of the module housing and through aperture 63 in the housingcover plate. Screws (not shown for clarity of illustration) can then bepassed through holes formed in holes 64 and 65 in the cover plate 60 andinserted into threaded holes 66 and 67 in the module housing 51. In thisassembled configuration, the scanning window 62 is completely formed andprovides access to the scanning element disposed within the housing. Inalternative embodiments, a transparent plate can be mounted over thescanning window to prevent dust, dirt and the like from entering thescanning mechanism embodied within the module housing.

[0344] Miniature Laser Beam Scanning System Formed By Arranging A LaserBeam Producing Module Of The Present Invention With A Laser BeamScanning Module

[0345] In FIG. 9, there is shown a miniature laser beam scanning systemformed by arranging the laser beam producing module 70 shown in FIG. 7with the laser scanning module 50, shown in FIG. 8A. This novelarrangement provides a laser scanning system for use in laser scanningengines of the general type disclosed, for example, in copendingapplication Ser. No. 08/292,237 filed Aug. 17, 1994, incorporated hereinby reference. As shown in FIG. 9, the output laser beam 71 from thelaser beam producing module 70 is directed onto the mirror on the lightdeflecting element (e.g. mirror) 55 within the laser scanning module 50.As the scanning element oscillates about its anchored base portion, thelaser beam 71A reflected off the mirror element 55 is scanned over thescanning region of the scanning system. Modules 70 and 50 can be mountedupon optical bench of various types employed, for example, for bar codesymbol scanning systems, and the like.

[0346] Integrated Laser Beam Producing And Scanning Module According ToA First Illustrative System Embodiment Of The Present Invention

[0347] In FIGS. 10A, 10B and 10C, a laser scanning device is shown,wherein the laser scanning subsystem shown in FIG. 8A is integrated witha laser beam producing subsystem of FIG. 7A. As shown, integratedscanning device 80 comprises an assembly of subcomponents, namely: amodule housing 81 made of lightweight plastic and serving as an opticalbench for the optical components within the laser beam producing andscanning systems alike; a VLD 82 mounted to a VLD heat-sinking plate 83through aperture 83A and producing a visible laser beam havingelliptical, eccentric, divergent, and astigmatic beam characteristics inresponse to a voltage source applied to terminals 82A by way of aflexible circuit or other conductive structures well known in the art; amounting bracket 84 having an aperture 84A for receiving a portion ofthe casing of the VLD 82 and a plane surface 84B affixing the associatedheat-sinking plate 83 thereto, and also having side projections 84D and84E for slidable receipt within spaced apart recesses 85B and 85C formedin the rear portion of the module housing 81; a collimating lens L1 86for focusing the laser beam produced from the VLD; fixedspatial-frequency HOE H1 88, securely mounted within a first mountingslot 89 formed in the module housing 81, for modifying the beamcharacteristics of the laser beam output from collimating lens L1 86;fixed spatial-frequency HOE H2 90, securely mounted within a secondmounting slot 91 formed in the module housing 81, for modifying the beamcharacteristics of the laser beam produced from HOE H1 to produce theoutput laser beam; a radiation-absorbing wall surface 92 formed in themodule housing, aligned with the zeroeth-order diffraction beam from HOEH1, and absorbing the zeroeth-order diffraction beam produced from HOEH1; electromagnetic (i.e. coil) 52 mounted within recess 93 in themodule housing, for producing a magnetic force field in response toelectrical current supplied to the input terminals thereof; scanningelement 54 supporting light deflecting element (e.g. mirror, hologram,refractive element, etc.) 55 on the front surface of its free end, andpermanent magnetic element 56 on the rear surface of its free end;mounting plates 57 and 58 for clamping the base portion of the scanningelement 54, and mounting the same within recess 94 formed within themodule housing 81; and a housing cover plate 95 for attachment to thetop surface 96 of the module housing 81, and securing the laser beamproducing and scanning mechanism components therewithin, while forming ascanning window 97 through which a scanned laser beam can be projectedout into a scan field for scanning.

[0348] In FIG. 10D, the subcomponents of integrated scanning engine areshown mounted within a miniature housing 99 having a base portion 99Aand cover plate 99C. Typically, the length, and width dimensions of thehousing 99 will be substantially smaller than a matchbox and can berealized as small as a sugar-cube using presently available enablingtechnology. As shown, a plastic window or filter 100 can be mounted overthe scanning window to protect entry of dust, dirt and the like into theinterior of the scan engine where there are optical components. Modulehousing 81 can be mounted to the bottom half of the scan engine housing99A shown in FIG. 10D. The scan engine can include a photodetector,analog and digital signal processing circuits 101 realized or printedcircuit boards 102 and 103, as taught in copending application Ser. No.08/292, 237 filed on Aug. 17, 1994.

[0349] Laser Beam Producing Module For Producing A Stigmatic Laser BeamHaving Focus Control, Controlled Aspect-Ratio and Zero Beam Dispersion(CASE B)

[0350] In FIGS. 11A, 11B and 11C, an illustrative embodiment of thelaser beam production System Embodiment Nos. 2 and 6 of FIGS. 2B and 2F)is disclosed. It is understood, however, that designs according toSystem Embodiments 3, 7, 9 and 11 may be used as well in theconstruction of this class of laser beam producing module.

[0351] As shown in FIGS. 11A through 11C, this optical system isrealized in the form of a miniature laser beam producing module 110comprising an assembly of subcomponents, namely: a module housing 111made of lightweight plastic and serving as an optical bench for theoptical components within the laser beam producing system; a VLD 112mounted to a VLD heat sinking plate 113 through aperture 113A andproducing a visible laser beam having elliptical, eccentric, divergentand astigmatic beam characteristics in response to a voltage sourceapplied to terminals 112A by way of a flexible circuit or like structurewell known in the art; a mounting bracket 114 having an oversizedaperture 114A for receiving a portion of the casing of the VLD 112 andplanar surface 114B for affixing the associated heat-sinking plate 113thereto, and also having side projections 114C and 114D for slidablereceipt within spaced apart recesses 115C and 115D formed in the rearportion of the module housing; a focusing lens L1 116 for focusing thelaser beam produced from the VLD; a bore 117 formed in module housing111 for mounting lens L1 116 therein; fixed spatial-frequency HOE H1118, securely mounted within a first mounting slot 119 formed in themodule housing 111, for modifying the beam characteristics of the laserbeam output from focusing lens L1 116; fixed spatial-frequency HOE H2120, fixedly mounted within a second mounting slot 121, formed in themodule housing III, for modifying the beam characteristics of the laserbeam produced from HOE H1; a focusing lens L2 122 mounted within alens-support bracket 123, slidably mounted within a third mounting slot124 formed in the module housing, for adjustable movement of lens L2 122along the optical axis of HOE H2 120 to adjust the focal-length ofoutput laser beam; a radiation-absorbing wall surface 126 formed in themodule housing, aligned with the zeroeth-order diffraction beam from HOEH1, and absorbing the zeroeth-order diffraction beam produced from HOEH1; and a housing cover plate 127 for attachment to the top portion ofthe module housing 111 and securing HOEs H1 and H2 and focusing lens L2therein.

[0352] In an illustrative embodiment of this system design, VLD 112 canbe realized using a SONY Model SLD1122VS laser diode, the focusing lensL1 116 can be realized using a 4.35 mm lens, and the focusing lens L2122 can be realized using a 250 mm lens, to provide an output focaldistance of about 10 inches from the module. The HOEs H1 and H2 can bemade using DCG recording material, of 5 microns film thickness, at aconstruction wavelength of 480 nanometers. These volume transmissionholograms can be mounted between a pair of ultra-small plates made fromfloat glass. It is understood, however, that other embodiments of thissystem design can be made using different types of components andmaterials, having different design parameters selected or determined forthe particular application at hand.

[0353] As shown in FIG. 11C, during assembly and alignment of the laserbeam producing module 110, the distance between VLD 112 and lens D1 116is adjusted by sliding the VLD mounting bracket 114 within the pair ofrecesses 115C and 115D in the module housing, and the distance betweenthe lens L2 122 and HOE H2 120 is adjusted by sliding lens-supportbracket 124 within the recess 124 in module housing along the opticalaxis of HOE H2. As will be explained in greater detail hereinafter,these parameter adjustment mechanisms are employed while the opticssystem is mounted on an optical bench specially crafted for aligningsuch parameters.

[0354] Laser Beam Producing Module For Producing A Stigmatic Laser BeamHaving Focus Control Controlled Aspect-Ratio, Zero Beam Dispersion, andAdjustable Focal-Length (CASE C)

[0355] In FIGS. 12A, 12B and 12C, an illustrative embodiment of thelaser beam production System Embodiment Nos. 4 and 8 of FIGS. 2D and 2H)is disclosed. It is understood, however, that such a design can berealized using System Embodiment Nos. 10 and 12, as well.

[0356] As shown in FIGS. 12A, 12B and 12C, this optical system isrealized in the form of a miniature laser beam producing module 130comprising an assembly of subcomponents, namely: a module housing 135made of lightweight plastic and serving as an optical bench for theoptical components within the laser beam producing system; a VLD 131mounted to a VLD heat sinking plate 132 through aperture 132A andproducing a visible laser beam having elliptical, divergent, eccentric,and astigmatic beam characteristics in response to a voltage sourceapplied to terminal 131 A by way of a flexible circuit or likeconductive elements well known in the art; a mounting bracket 133 havingan aperture 133A for receiving a portion of the casing of the VLD 131and, a planar surface 133B for affixing the associated heat-sinkingplate 132 thereto, and also having side projections 133C and 133D forslidable receipt within spaced apart recesses 135C and 135D formed inthe rear portion of the module housing; a focusing lens L1 136 forfocusing the laser beam produced from the VLD; a bore 137 for mountinglens 136 within the module housing; fixed spatial-frequency HOE H1 138,securely mounted within a first mounting slot 139 formed in the modulehousing 135, for modifying the beam characteristics of the laser beamoutput from focusing lens L1 136; fixed spatial-frequency HOE H2 140,mounted within a HOE-support bracket 141 that is slidably mounted withina second mounting slot 142 formed in the module housing 135, foradjustable movement relative to HOE H1 138 (during assembly/alignment)in order to modify the beam characteristics of the laser beam producedfrom HOE H1; a focusing lens L2 143 mounted within a lens-supportbracket 144 that is slidably mounted within a third mounting slot 145formed in the module housing, for adjustable movement along the opticalaxis of the system; a radiation-absorbing wall surface 146 formed in themodule housing, aligned with the zeroeth-order diffraction beam from HOEH1, and absorbing the zeroeth-order diffraction beam produced from HOEH1; and a housing cover plate 147 for attachment to the top portion 148of the module housing 135 and securing HOEs H1 and H2 and focusing lensL2 therein.

[0357] In an illustrative embodiment, the VLD can be realized using aSONY Model SLD1122VS laser diode, the focusing lens L1 can be realizedusing a 4.35 mm lens, and the focusing lens L2 is realized using a 250mm lens. The HOEs H1 and H2 can be made using DCG recording material, ofabout 5 microns thickness, at construction wavelength 488 nanometers.These volume transmission holograms can be mounted between a pair ofultra-small plates made from float glass. It is understood, however,that other embodiments of this system design can be made using differenttypes of components and materials, having different design parametersselected or determined for the particular application at hand.

[0358] As shown in FIG. 12C, during assembly and alignment of the laserbeam producing module 130, the distance between VLD 131 and lens L1 136is adjusted by sliding the VLD mounting bracket 133 within the pair ofrecesses 135C and 135D in the module housing, and the distance betweenthe lens L2 and HOE H2 140 is adjusted by sliding lens-support bracket144 within the recess 145 in module housing, and the distance betweenHOE H2 and HOE H1 is adjusted by sliding HOE support bracket M1 withinrecess 142 in the module housing. As will be explained in greater detailhereinafter, these parameter adjustment mechanisms are employed whilethe system is mounted on an optical bench specially crafted for aligningsuch parameters.

[0359] The design methods of the present invention provide a way ofdetermining the design and construction parameters for the laser beamproducing system of the present invention. However, by virtue of thefact that properties of the VLD are not easily ascertainable inpractice, such methods cannot be used to compute the distance betweenthe VLD and lens L1 which results in an output laser beam having zerodispersion and a desired aspect ratio.

[0360] The Parameter Adjustment System Used During The Module Assemblyand Alignment Procedure Of The Present Invention

[0361] In FIG. 13, a computer-controlled parameter adjustment system ofthe present invention is shown. For purposes of illustration only, thissystem is shown in FIG. 13 with a laser beam producing module of FIGS.12A-12C (embodying System Embodiment No. 4 for illustration only)mounted to the fixtures of the system. This case was selected becausethis module requires the maximum number of parameters to be adjusted,thus implicating all of the functions of the parameter adjustmentsystem. As will be illustrated, however, the parameter adjustment systemcan be used to adjust the parameters of any one of the illustratedembodiment of the present invention in a rapid, highly efficient manner,thereby making the laser beam producing modules hereof suitable for massproduction.

[0362] As shown in FIG. 13, the parameter adjustment system 150comprises a number of subsystems and subcomponents, namely: a modulesupport platform 151 for supporting and translating (in the z directionduring the “loading stage”) the module housing (e.g. 135) of each laserbeam producing module (being assembled and adjusted); a VLD supportplatform 154 for adjustably supporting the VLD (and its mountingstructure) along three-coordinate axes relative to the stationary modulehousing support platform 151 and lens L1; a lens L2 support platform 155for supporting and translating second lens L2 of the laser beamproducing module along one-coordinate axis relative to the stationarymodule housing support platform 151; a HOE support platform 156 forsupporting and translating HOE H2 of the laser beam producing modulealong one-coordinate axis (i.e. optical axis) relative to the modulehousing support platform 151 (i.e. along the optical axis of thesystem); a beam profiler 157 (such as, for example, Model 0180-XYS BeamScan from Photon, Santa Clara, Calif.) having a beam scan displaymonitor 158 connected thereto; a quadrant detector 159 having a quadrantdetector display 160 connected thereto; a first computer-controlledtranslation mechanism 161A for translating the VLD support platform 154relative to module housing support platform 151 during analysis of thelaser beam output from the HOE-based subsystem of the laser beamproducing module 153 using the beam scanner 157 and quadrant detector159; a second computer-controlled translation mechanism 161B fortranslating the lens L2 support platform 155 relative to module housingsupport platform 151 during analysis of the laser beam output from theHOE-based subsystem of the laser beam producing module 153 using thebeam scanner 157 and the quadrant detector 159; and a thirdcomputer-controlled translation mechanism 161C for translating the HOEsupport platform 156 relative to module housing support platform 151during analysis of the laser beam output from the HOE-based subsystem ofthe laser beam producing module 153 using the beam scanner 157 and thequadrant detector 159. As will be explained hereinafter, certain ofthese subsystems are not employed when adjusting the parameters ofparticular laser beam producing modules of the present invention, whileother of these subsystem are employed when aligning the components ofother types of laser beam producing modules. Such details will bedescribed below.

[0363] Method of Assembling and Aligning The Subcomponents Of Laser BeamProducing Systems Of The Illustrative System Embodiments Of The PresentInvention Design For Instances Where

[0364] Focusing Control Is Desired And Astigmatism Correction AndDelta-Focusing are Not Desired (System Embodiments Nos. (1) and (5):CASE A In general, when assembling a laser beam producing module basedon System Embodiments Nos. 1 and 5, the below described parameteradjustment procedure can be used in conjunction with the parameteradjustment system of FIG. 13. The procedure comprises a pre-alignmentstage and an alignment stage. During the prealignment stage, the variousoptical components of the laser beam producing module are installedwithin their respective mounting locations within the module housing, orwithin support structure associated with the parameter adjustment system150. During the alignment stage, the VLD and lens L1 are aligned inorder to achieve the performance characteristics considered during thedesign stage. Referring to FIG. 14, the details of each of these stageswill be described below for System Embodiment Nos. 1 and 5. In FIG. 14,the module of FIGS. 7A-7C is shown mounted within the fixture of theparameter adjustment system as it embodies System Embodiment Nos. 1 and5 in their entirety.

[0365] Pre-alignment Stage of the Assembly Procedure For SystemEmbodiment Nos. 1 and 5

[0366] The first step of the pre-alignment stage of the system assemblyprocedure involves press fitting the VLD 32 into VLD heat-sink plate 33so that the VLD junction is arranged in a predetermined orientationrelative to the VLD heat-sink plate.

[0367] The second step of the prealignment stage involves mounting HOEH1 (39) and HOE H2 (41) into their appropriate mounting slots 40 and 42formed within module housing 31. Thereafter, the HOEs can be glued orotherwise fixed in position. The third step of the prealignment stageinvolves inserting lens L1 into the lens recess (e.g. pocket) formedwithin the module housing. Thereafter, the lens L1 can be glued orotherwise fixed in position.

[0368] The fourth step of the prealignment stage involves placing theVLD mounting bracket (i.e. yoke) 36 into appropriate recesses 37C and37D formed in the module housing. Notably, the VLD mounting bracket isheld within such recesses by frictional fit and can only be translatedalong (z) axis of the parameter alignment system (i.e. the x and ydirections being fixed by the geometry of these recesses.

[0369] The fifth step of the prealignment stage involves placing themodule housing 31 onto the module housing support platform 151 so thatpins on the bottom surface of the housing module 31 align withcorresponding holes formed on the housing module support platform 151.When housing module 31 is installed in the manner described above, themodule housing 31 is then clamped to the module housing support platform151 by way of screws, pressurized clamps or other releasable fasteningdevices.

[0370] The sixth step of the prealignment stage involves clamping theyoke 36 to affixed holder 164.

[0371] The seventh and last step of the prealignment stage involvesattaching the VLD 32 to VLD support platform 154 of the parameteralignment system. In the preferred embodiment, this step can be achievedby sliding the leads of the VLD into a connector provided on the VLDsupport platform and secured by clamping, etc. The VLD support platform154 is capable of movement along the x, y and z axes of the parameteradjustment system 150.

[0372] The Alignment Stage of the Assembly Procedure For SystemEmbodiments Nos. 1 and 5

[0373] The first step of the alignment stage of the system assemblyprocedure involves sliding the module housing support platform 151towards VLD support platform 151 under the control of microcontroller161 until the VLD 32 is positioned within oversized aperture 36A formedwithin the VLD support 36 positioned within the recesses of the modulehousing. Notably, at this “load” position, the VLD 32 is free to movewithin the x and y plane by virtue of the oversized aperture in the VLDmounting yoke, and also along the z axis by virtue of clearance providedbetween the premounted lens D1 and the outer face of the VLD mountingyoke. As will become apparent hereinafter, such clearance enables theoptical axis of each loaded VLD to be aligned with the optical axis oflens D1 as well as attaining the required distance which achieves thedesired focus (for System Embodiment Nos. 1 and 5) or control ofastigmatism (for all System Embodiments except Nos. 13 and 14) asspecified during the design stage described in detail above.

[0374] The second step of the alignment stage of the procedure involveslocking the position the module housing support platform 151 relative tothe underlying optical bench 151 (arranged in its “loaded”configuration). This locking operation can be carried out using acomputer-controlled locking mechanism 163 known in the art.

[0375] The third step of the alignment stage of the procedure involveslocking the VLD heat-sink plate 32 to the VLD support platform 154locking using mechanism 162 so that the VLD heat-sink plate is preventedfrom undergoing rotation in the x-y plane during alignment of the VLDrelative to the lens L1 during the subsequent steps of the alignmentprocedure. This condition will ensure that the VLD junction is preventedfrom rotation during the alignment procedure, which may involvetranslation of the VLD junction in the x, y and/or z axes of the systemin order to secure the performance parameters of the module establishedduring the design stage.

[0376] The fourth step of the alignment stage of the procedure involvesapplying a biasing force on the VLD support yoke 36 (in the direction ofthe VLD heat-sink plate 33) so that the plate-like portion of the VLDsupport yoke gently engages the VLD heat-sink plate 33 in order that thesurface of the VLD heat-sink plate and planar portion of the VLD supportyoke assume the same z coordinate position during x, y alignmentoperations, while permitting relative movement between these twoplate-like structures along the x-y plane of the system.

[0377] The fifth step of the alignment stage of the procedure involvessupplying electrical power to the VLD 32 so that it produces a laserbeam which is transmitted through lens L1 and HOEs H1 and H2.

[0378] The sixth step of the alignment stage of the procedure involvestranslating the VLD support platform 154 in the x-y plane until theoutput laser beam strikes the center of the quadrant detector 159, whichhas been prealigned relative to the locked-in-position module housing 31so that first diffraction order beam from HOE H2 (i.e. the optical axisthereof disposed in the plane of diffraction at diffraction angleθ_(d2)) passes through the center of the quadrant-type photodetector159. When the output laser beam strikes the center of the quadrant-typephotodetector, then the design geometry will be achieved, resulting inminimum beam dispersion and the desired amount of beam shaping bydesign. Also optimal output power will be transmitted from the modulealong the optical axis of the system. This condition is based on thereasonable assumption that the diffraction efficiency of HOEs H1 and H2will be maximum along the first diffraction order by design, andcharacteristic wavelength of the VLD is substantially the same as thereconstruction wavelength of HOEs H1 and H2. Notably, this on-centeraligned position can be visually detected when the indicator dot on thequadrant detector display unit 160 is aligned with the crosshairthereof. Completion of this step of the procedure will ensure thatoutput power from the laser beam producing module will be as close tothe output of the VLD as is practically possible, as well as ensuringthat the design requirements have been satisfied.

[0379] The seventh step of the alignment stage of the procedure involvesgluing or otherwise permanently securing the x-y position of the VLDheat-sinking plate 33 and VLD support bracket 36 in the positiondetermined during the step above. Thereafter, the biasing force appliedduring the above step of the procedure can be removed.

[0380] The eighth step of the alignment stage of the procedure involvesadjusting the position of the subassembly (comprising the VLD 32, theVLD heat-sink plate 32 and the VLD support yoke 36) along the z axis ofthe parameter adjustment system while monitoring the output laser spotat the desired focal length of the module using a beam profiler (i.e.profiling instrument) 157, as identified above. When the spot size ofthe output laser beam at the desired focal length is minimum (alongeither the x or y axis of the system, not both), then VLD support yoke36 is glued or otherwise fixed in position relative to the modulehousing 31. Thereafter, the housing cover plate 44 is fastened upon themodule housing and then the aligned laser beam producing module isremoved from the parameter adjustment system and is ready for use in thesystem 150 for which it has been designed.

[0381] Method Of Assembly And Aligning The Subcomponents Of Laser BeamProducing Systems Of The Illustrative System Embodiments Of The PresentInvention Designed For Instances Where Astigmatism Correction and FocusControl are Desired, but Not The Adjustment of the Laser Beam FocalLength: System Embodiment Nos. (2) (3), (6), (7), (9) and (11): CASE B

[0382] In general, when assembling a laser beam producing module basedon System Embodiments Nos. 2 and 6, the parameter adjustment procedureof the present invention can be carried out on the module design shownin FIGS. 11A-11C supported upon the parameter adjustment system of FIG.13. When assembling a laser beam producing module based on SystemEmbodiments Nos. 9 and 11, the parameter adjustment procedure of thepresent invention can be carried out on the module design similar tothat shown in FIGS. 11A-11C (but with lens L2 disposed between H1 andh2) supported upon the parameter adjustment system of FIG. 13. Also,when assembling a laser beam producing module based on SystemEmbodiments Nos. 3 and 7, the parameter adjustment procedure of thepresent invention can be carried out on the module design similar to themodule shown in FIGS. 12A through 12C (without lens L2) supported uponthe parameter adjustment system of FIG. 13.

[0383] For each of these groups of system embodiments, the assemblyprocedure comprises a prealignment stage and an alignment stage. Duringthe prealignment stage, the various optical components of the laser beamproducing module are installed within their respective mountinglocations within the module housing, or within support structureassociated with the parameter adjustment system 150. During thealignment stage, the VLD and lens L1 are aligned, as well as HOE H2relative to HOE H1 (and L2 where applicable) in order to achieve theperformance characteristics specified during the design stage. Detailsof each of these stages will be described below for System EmbodimentNos. 2 and 6, 9 and 11, 3 and 7, with reference to FIG. 15.

[0384] Pre-Alignment Stage of the Assembly Procedure For SystemEmbodiment Nos. 2 and 6

[0385] The first step of the prealignment stage of the system assemblyprocedure involves press fitting the VLD 112 into VLD heat-sink plate113 so that the VLD junction is oriented in it predetermined orientationrelative to the VLD heat-sink plate.

[0386] The second step of the prealignment stage involves mounting HOEH1 and HOE H2 into their appropriate mounting slots 115C and 115D formedwithin module housing 111. Thereafter, the HOEs can be glued orotherwise fixed in position.

[0387] The third step of the prealignment stage involves inserting lensL1 into the lens recess (e.g. bore) 117 formed within the modulehousing. Thereafter, the lens L1 can be glued or otherwise fixed inposition.

[0388] The fourth step of the prealignment stage involves placing theVLD mounting yoke 114 into appropriate recesses 115C and 115D formed inthe module housing. Notably, the VLD mounting yoke is held withinrecesses 115C and 115D by frictional fit and can only be translatedalong z axis of the parameter alignment system (i.e. the x and ydirections being fixed by the geometry of the recesses.

[0389] The fifth step of the prealignment stage involves placing themodule housing 111 into the module housing support platform 151 so thatpins on the bottom surface of the housing module align withcorresponding holes formed on the housing module support platform 151.When housing module 111 is installed in the manner described above, themodule housing is then clamped to the module housing support platform151 by way of screws, pressurized clamps or other releasable fasteningdevices.

[0390] The sixth step of the prealginment stage involves placing themounting yoke 114 on its support platform and clamping the same inplace.

[0391] The seventh and last step of the prealignment stage involvesattaching the VLD 112 to VLD support platform 151 of the parameteralignment system. In the preferred embodiment, this step can be achievedby sliding the leads of the VLD into a connector provided on the VLDsupport platform. The VLD support platform 154 is capable of movementalong the x, y and z axes of the parameter adjustment system 150.

[0392] Alignment Stage of the Assembly Procedure For System EmbodimentNos. 2 and 6

[0393] The first step of the alignment stage of the system assemblyprocedure involves sliding the module housing support platform 151towards VLD support platform 154 under the control of microcontroller161 until the VLD is positioned within oversized aperture 114A formedwithin the VLD support yoke 114 positioned within the recesses of themodule housing. Notably, at this “load” position, the VLD is free tomove within the x and y plane by virtue of the oversized aperture in theVLD mounting yoke, and also along the z axis by virtue of clearanceprovided between the premounted lens L1 and the outer face of the VLDmounting yoke. As will become apparent hereinafter, such clearanceenables the optical axis of each loaded VLD to be aligned with respectto the optical axis of lens L1.

[0394] The second step of the alignment stage of the procedure involveslocking the position the module housing support platform 151 relative tothe underlying optical bench (arranged in its “loaded” configuration).This locking operation can be carried out using locking mechanism 162known under computer control.

[0395] The third step of the alignment stage of the procedure involveslocking the VLD heat-sink plate to the VLD support platform 154 so thatthe VLD heat-sink plate is prevented from undergoing rotation in the x-yplane during alignment of the VLD relative to the lens L1 during thesubsequent steps of the alignment procedure. This condition will ensurethat the VLD junction is prevented from rotation during the alignmentprocedure, which may involve translation of the VLD junction in the x, yand/or z axes of the system in order to secure the performanceparameters of the module established during the design stage.

[0396] The fourth step of the alignment stage of the procedure involvesapplying a biasing force on the VLD support yoke 114 (in the directionof the VLD heat-sink plate 113) so that the plate-like portion of theVLD support yoke gently engages the VLD heat-sink plate 113 in orderthat the surface of the VLD heat-sink plate and planar portion of theVLD support yoke assume the same z coordinate position during x, yalignment operations, while permitting relative movement between thesetwo plate-like structures along the x-y plane of the system.

[0397] The fifth step of the alignment stage of the procedure involvessupplying electrical power to the VLD 112 so that it produces an outputlaser beam which is transmitted through lens L1 and HOEs H1 and H2.

[0398] The sixth step of the alignment stage of the procedure involvestranslating the VLD support platform 154 in the x-y plane until theoutput laser beam strikes the center of the quadrant photodetector 159,which has been prealigned relative to the locked-in-position modulehousing 111 so that first diffraction order beam from HOE H2 (i.e. theoptical axis thereof disposed in the plane of diffraction at diffractionangle θ_(d2)) passes through the center of the quadrant-typephotodetector. When the output laser beam strikes the center of thequadrant-type photodetector, then the design geometry will be achieved,resulting in minimum beam dispersion and the desired amount of beamshaping by design. Also optimal output power will be transmitted fromthe module along the optical axis of the system. This condition is basedon the reasonable assumption that the diffraction efficiencies of HOEsH1 and H2 120 will be maximum along the first diffraction order bydesign, and characteristic wavelength of the VLD is substantially thesame as the reconstruction wavelength of HOEs H1 and H2. Notably, thison-center aligned position can be visually detected when the indicatordot on the quadrant detector display unit 160 is aligned with thecross-hair on the display surface thereof. Completion of this step ofthe procedure will ensure that the output power of the laser beamproducing module will be as close to the output of the VLD as ispractically possible, as well as ensuring that the design requirementshave been satisfied.

[0399] The seventh step of the alignment stage of the procedure involvesgluing or otherwise permanently securing the x-y position of the VLDplate and VLD support yoke in the position determined during the stepabove. Thereafter, the biasing force applied during the above step ofthe procedure can be removed.

[0400] The eighth step of the alignment stage of the procedure involvesadjusting the position of the subassembly (comprising the VLD 112, theVLD heat-sink plate 113 and the VLD support yoke 114) along the z axisof the parameter adjustment system while monitoring the output laser atthe desired focal length of the module using beam profiling (scanning)instrument 157. When the spot size of the output laser beam (at someunknown location along the optical axis HOE H2) is minimum in both the xand y dimensions, then VLD support yoke 114 is glued or otherwise fixedin position relative to the module housing 111. Notably, the beamprofiling instrument will have to be moved along the optical axis of HOEH2 to detect this condition, in which the output laser beam is free ofastigmatism. While the output beam may still have ellipticalcross-sectional characteristics along its direction of propagation, itsbeam cross-section will be minimum for both dimensions at this detectedpoint which, by definition, is a stigmatic beam. Thereafter, the VLDsupport yoke is glued or otherwise fixed to the module housing 111.

[0401] The ninth step of the alignment stage of the procedure involvesinserting lens support bracket 123, containing prespecified lens L2,into recess 124 formed within the front end of the module housing 111.

[0402] The tenth step of the alignment stage of the procedure involvesadjusting the focal length of the module by translating lens L2 alongthe optical axis (or adjusting the combined focal length of a lens pair)while monitoring the output laser beam (at the desired focal length ofthe module set during design) until the spot size of the laser isminimum. In one illustrative embodiment, this is achieved by slidinglens L2 relative to HOE H2. In instances where multiple lens elementsare used to construct L2, the spacing if such lenses can be varied toimpart the desired focal length to the lens system L2. Notably, in someinstances, it may also be desirable or necessary to adjust the (x,y)position of the L2 along the optical axis of the system. Thereafter, thelens L2 mounting bracket is glued or otherwise fixed relative to themodule housing. Then the housing cover plate 127 is then fastened uponthe top of the module housing and then the aligned laser beam producingmodule is removed from the parameter adjustment system and is ready foruse in the system for which it has been designed.

[0403] Pre-Alignment/Alignment Stage of the Assembly Procedure ForSystem Embodiment Nos. 9 and 11

[0404] The prealignment stage for System Embodiments Nos. 9 and II issimilar to that described for System Embodiments 1, 5, 13 and 14 abovewith several exceptions. Foremost, in System Embodiment Nos. 9 and 11,second lens L2 is disposed between H1 and H2. Thus, a module similar tothat shown in FIGS. 11A-11C, but with second lens L2 disposed betweenHOEs H1 and H2, could be used to realize such a system design. Notably,the design of such a module will enable the second lens L2 to beinstalled within its modified module housing after completing thealignment procedure described above. When the second lens L2 isinstalled within the module housing, the focal length of the outputlaser beam can be set by translating lens L2 along the optical axis (oradjusting the focal-length of second lens L2 in appropriate cases).

[0405] Pre-Alignment And Alignment Stages Of The Assembly Procedure ForSystem Embodiment Nos. 3 and 7

[0406] The prealignment stage of the assembly procedure for SystemEmbodiment Nos. 3 and 7 is different than that described for SystemEmbodiment Nos. 2 and 6 above, in two significant ways. First, HOE H2 isa variable spatial-frequency HOE (having focusing power) which ismounted in a HOE support bracket enabling its principal plane to betranslated along its optical axis relative to the principal plane of HOEH1 without modifying the tilt angle ρ therebetween. Secondly, in SystemEmbodiment Nos. 3 and 7, there is no second lens L2 as required inSystem Embodiments Nos. 2 and 6. While such structural differencessimplify the prealignment stage of the assembly process, they do notalter the procedure for aligning the VLD junction along the x and y axesof the system to minimize beam dispersion, or along the z axis toeliminate beam astigmatism. Notably, after eliminating beam dispersionand correcting for astigmatism, HOE H2 can be translated along itsoptical axis to set the focal length (i.e. focus) of the output laserbeam to that specified during design.

[0407] Method Of Assembling And Aligning The Subcomponents Of Laser BeamProducing Systems Of The Illustrative System Embodiments Of The PresentInvention Designed For Instances Where Focus Control AstigmatismCorrection and Delta-Focusing are Desired: System Embodiments Nos. (4),(8), (10) and (12): Case C

[0408] In general, when assembling a laser beam producing module basedon System Embodiments Nos. 4 and 8, the parameter adjustment procedureof the present invention can be carried out on the module design shownin FIGS. 1A-11C supported upon the parameter adjustment system of FIG.13. When assembling a laser beam producing module based on SystemEmbodiments Nos. 10 and 12, the parameter adjustment procedure of thepresent invention can be carried out on the module design similar tothat shown in FIGS. 11A-11C (but with lens L2 disposed between H1 andH2) supported upon the parameter adjustment system of FIG. 13.

[0409] For each of these groups of system embodiments, the assemblyprocedure comprises a prealignment stage and an alignment stage. Duringthe prealignment stage, various optical components of the laser beamproducing module are installed within their respective mountinglocations within the module housing, or within support structureassociated with the parameter adjustment system 150. During thealignment stage, the VLD and lens L1 are aligned relative to each other,the focusing lens L2 is aligned relative to HOE H2, and the HOE H2 isaligned relative to HOE H1, in order to achieve the performancecharacteristics specified during the design stage. Details of each ofthese stages will be described below for System Embodiment Nos. 4, 8, 10and 12, with reference to FIG. 16.

[0410] Pre-Alignment Stage of the Alignment Procedure For SystemEmbodiment Nos. 4 and 8

[0411] The first step of the prealignment stage of the system assemblyprocedure involves press fitting the VLD 131 into VLD heat-sink plate132 so that the VLD junction is oriented in it predetermined orientationrelative to the VLD heat-sink plate.

[0412] The second step of the prealignment stage involves mounting HOEH1 and HOE H2 (supported in its mounting bracket 141) into theirappropriate mounting slots 139 and 142 formed within module housing 135.Thereafter, HOE H1 can be glued or otherwise fixed in position, whileHOE H2 is permitted to moved along its along its optical axis within themodule housing.

[0413] The third step of the prealignment stage involves inserting lensL1 into the lens recess (e.g. pocket) formed within the module housing,so that the planar side of the lens L1 is mounted incident the VLD 131.Thereafter, the lens L1 can be glued or otherwise fixed in position.

[0414] The fourth step of the prealignment stage involves placing theVLD mounting bracket 133 into appropriate recesses 133C and 133D formedin the module housing. Notably, the VLD mounting yoke is held withinrecesses 133C and 133D by frictional fit and can only be translatedalong z axis of the parameter alignment system (i.e. the x and ydirections being fixed by the geometry of the recesses.

[0415] The fifth step of the prealignment stage involves placing themodule housing 135 into the module housing support platform 151 so thatpins on the bottom surface of the housing module align withcorresponding holes formed on the housing module support platform 151.When housing module 135 is installed in the manner described above, itis then clamped to the module housing support platform 151 by way ofscrews, pressurized clamps or other releasable fastening devices.

[0416] The sixth step of the prealignment stage involves placing themounting youe 114 on its support and clamping the same.

[0417] The seventh and last step of the prealignment stage involvesattaching the VLD 131 to VLD support platform 154 of the parameteralignment system. In the preferred embodiment, this step can be achievedby sliding the leads of the VLD into a connector provided on the VLDsupport platform. The VLD support platform 154 is capable of movementalong the x, y and z axes of the parameter adjustment system 150.

[0418] Alignment Stage of the Assembly Procedure For System EmbodimentNos. 4 and 8

[0419] The first step of the alignment stage of the procedure involvessliding the module housing support platform 151 towards VLD supportplatform 154 under the control of microcontroller 161 until the VLD ispositioned within oversized aperture 133A formed within the VLD supportbracket 133 positioned within the recesses of the module housing.Notably, at this “load” position, the VLD is free to move within the xand y plane by virtue of the oversized aperture in the VLD mountingyoke, and also along the z axis by virtue of clearance provided betweenthe premounted lens L1 and the outer face of the VLD mounting yoke. Aswill become apparent hereinafter, such clearance enables the opticalaxis of each loaded VLD to be aligned with respect to the optical axisof lens L1 in a manner required to achieve minimal beam dispersion andthe desired aspect-ratio specified during the design stage describedabove.

[0420] The second step of the alignment stage of the procedure involveslocking the position the module housing support platform 151 relative tothe underlying optical bench 152 (arranged in its “loaded”configuration). This locking operation can be carried out using lockingmechanism 162 computer control.

[0421] The third step of the alignment stage of the procedure involveslocking the VLD heat-sink plate 132 to the VLD support platform 154 sothat the VLD heat-sink plate is prevented from undergoing rotation inthe x-y plane during alignment of the VLD 131 relative to the lens L1during the subsequent steps of the alignment procedure. This conditionwill ensure that the VLD junction is prevented from rotation during thealignment procedure, which may involve translation of the VLD junctionin the x, y and/or z axes of the system in order to secure theperformance parameters of the module established during the designstage.

[0422] The fourth step of the alignment stage of the procedure involvesapplying a biasing force on the VLD support bracket 133 (in thedirection of the VLD heat-sink plate) so that the plate-like portion ofthe VLD support yoke gently engages the VLD heat-sink plate 132 in orderthat the surface of the VLD heat-sink plate and planar portion of theVLD support bracket 133 assume the same z coordinate position during x,y alignment operations, while permitting relative movement between thesetwo plate-like structures along the z-x plane of the system.

[0423] The fifth step of the alignment stage of the procedure involvessupplying electrical power to the VLD 131 SO that it produces an outputlaser beam which is transmitted through lens L1 and HOEs H1 and H2.

[0424] The sixth step of the alignment stage of the procedure involvestranslating the VLD support platform 154 in the x-y plane until theoutput laser beam strikes the center of the quadrant photodetector 159,which has been prealigned relative to the locked-in-position modulehousing 135 so that first diffraction order beam from HOE H2 (i.e. theoptical axis thereof disposed in the plane of diffraction at diffractionangle θ_(d2)) passes through the center of the quadrant-type detector159. When the output laser beam strikes the center of the quadrant-typephotodetector, then the design geometry will be achieved, resulting inminimum beam dispersion and the desired amount of beam shaping bydesign. Also optimal output power will be transmitted from the modulealong the optical axis of the system. This condition is based on thereasonable assumption that the diffraction efficiencies of HOEs H1 andH2 will be maximum along the first diffraction order by design, andcharacteristic wavelength of the VLD is substantially the same as thereconstruction wavelength of HOEs H1 and H2. Notably, this on-centeraligned position can be visually detected when the indicator dot on thequadrant detector display unit 160 is aligned with the cross-hair on thedisplay surface thereof. Completion of this step of the procedure willensure that output power of the laser beam producing module will be asclose to the output power of the VLD as is practically possible, as wellas ensuring that the design requirements have been satisfied.

[0425] The seventh step of the alignment stage of the procedure involvesgluing or otherwise permanently securing the x-y position of the VLDheat-sink plate 132 and VLD support bracket (yoke) 133 in the positiondetermined during the step above. Thereafter, the biasing force appliedduring the above step of the procedure can be removed.

[0426] The eighth step of the alignment stage of the procedure involvesadjusting the position of the subassembly (comprising the VLD 131, theVLD heat-sink plate 132 and the VLD support yoke 133) along the z axisof the parameter adjustment system while monitoring the output laser atthe desired focal length of the module using beam profiling instrument157. When the spot size of the output laser beam (at some unknownlocation along the optical axis HOE H2) is minimum in both the x and ydimensions, then VLD support yoke 133 is glued or otherwise fixed inposition relative to the module housing 135. Notably, the beam profilinginstrument will have to be moved along the optical axis of HOE H2 todetect this condition, in which the output laser beam is free ofastigmatism. While the output beam may still have ellipticalcross-sectional characteristics along its direction of propagation, itsbeam cross-section will be minimum for both dimensions at this detectedpoint which, by definition, is stigmatic beam. Thereafter, the VLDsupport yoke is glued or otherwise fixed to the module housing 135.

[0427] The ninth step of the alignment stage of the procedure involvesadjusting the position of HOE H2 relative to HOE H1 while monitoring thebeam cross-section at a focal point determined during the process) usingbeam profiling instrument 157. When the output laser beam is focused toa predetermined focal point, then the position of HOE H2 is glued orotherwise fixed relative to HOE Hi.

[0428] The tenth step of the alignment stage of the procedure wouldinvolve inserting lens support bracket 144, containing prespecified lensL2 143, into recess 145 formed within the front end of the modulehousing 135. In the illustrative embodiment, lens mounting bracket 144can be manually adjusted by a small adjustment screw or like mechanismembodied within the module housing. This adjustment mechanism allows theend-user to fine-tune the resulting focal length of the laser beamproducing module as required or desired by the application at hand. Insome instances, it is contemplated that the laser beam producing modulewill be installed within a larger system, in which the output stigmaticlaser beam from the module will be further modified for a particularapplication (e.g. scanning). In such cases, it is understood that thelaser beam producing module may be first removed from the module housingsupport platform 151 of the parameter adjustment system described above,and then installed within the larger system. Thereafter, the resultinglarger system can be mounted to a parameter adjustment system of thegeneral type described above in order to set the focal length of thelaser beam producing module so that the focal length of the resultingsystem is achieved. Clearly, there will be may ways in which tofine-tune the focal length of the laser beam producing module of SystemEmbodiment Nos. 4 and 8.

[0429] Then the housing cover plate 147 is fastened upon the top of themodule housing, and thereafter the aligned laser beam producing moduleis removed from the parameter adjustment system and is ready for use inthe system 150 for which it has been designed.

[0430] Pre-Alignment And Alignment Stages Of The Assembly Procedure ForSystem Embodiment Nos. 10 and 12

[0431] The prealignment stage of the assembly procedure for SystemEmbodiment Nos. 10 and 12 is different than that described for SystemEmbodiment Nos. 4 and 8 above, in one significant way. In particular, inSystem Embodiment Nos. 10 and 12, the second lens L2 is disposed betweenthe HOEs H1 and H2, rather than beyond the HOE H2, as shown in FIGS. 2Jand 2L. Such structural differences alter the prealignment stage of theassembly process slightly, as well as the procedure for aligning the VLDjunction along the x and y axes of the system to minimize beamdispersion, or along the z axis to eliminate beam astigmatism. Inparticular, beam dispersion is minimized while an “alignment HOE” withno optical power installed in the position of HOE H2, when theposition-adjustable lens L2 is not yet installed within the modulehousing. Astigmatism is corrected by adjusting the position of the VLDrelative to fixed lens L1 136. Then an average focal distance for thelaser beam producing module is set by inserting lens L2 and adjustingits position within its mounting recess. At this stage, the alignmentHOE is removed and HOE H2 is put into place and can be adjusted while onthe module housing platform to set a finely tuned focal distance for thelaser beam producing module, or alternatively, first installed within alarger optical system, and thereafter adjusted to fine tune the focallength of the module to achieve a particular design objective for thelarger optical system, as described hereinabove.

[0432] Method Of Assembly And Aligning The Subcomponents Of Laser BeamProducing Systems Of The Illustrative System Embodiments Of The PresentInvention Designed For Instances Where Astigmatism Correction Is DesiredBut Neither Focus Control nor Delta-Focusing Are Required: SystemEmbodiment Nos. (13) and (14): CASE D In general, when assembling alaser beam producing module based on System Embodiments Nos. 13 and 14,the parameter adjustment procedure of the present invention can becarried out on the module design similar to that shown in FIGS. 7A-7C(but with lens L1 being a focusing lens) supported upon the parameteradjustment system of FIG. 13, as shown in FIG. 17.

[0433] For this group of system embodiments, the assembly procedurecomprises a prealignment stage and an alignment stage. During theprealignment stage, various optical components of the laser beamproducing module are installed within their respective mountinglocations within the module housing, or within support structureassociated with the parameter adjustment system 150, as described inconnection with System Embodiment Nos. 1 and 5. During the alignmentstage, the (x,y) position of the VLD is aligned relative to the focusinglens L1 in order to achieve zero beam dispersion for the central ray ofthe beam and minimized for all others, using the (x,y) alignmentprocedure described hereinabove. Thereafter, the position of the VLD isadjusted along the z axis in order to eliminate astigmatism in theoutput laser beam using the z axis alignment procedure described above.Notably, in this System Embodiment, astigmatism elimination is achievedat the expense of the focus control, while minimizing beam dispersionand achieving a limited degree of aspect-ratio control.

[0434] Exemplary Systems and Devices Within Which The Laser BeamProducing System Of The Present Invention Can Be Embodied

[0435] The laser beam producing system of the present inventiondescribed in detail hereinabove may, in all of its various embodiments,be embodied within an infinite variety of systems requiring theproduction of a laser beam having predetermined beam characteristics,substantially free of dispersion. Hereinbelow are just a few exemplarysystems and devices within which the laser beam production system can beembodied in accordance with the principles of the present invention. Assuch, each such system provides a further embodiment of the presentinvention.

[0436] As illustrated in FIG. 18, any one of the laser beam producingdevices of the present invention can be incorporated in ahand-supportable laser scanning device As illustrated in FIG. 19, anyone of the laser beam producing devices of the present invention can beincorporated a fixed-projection type laser scanning system.

[0437] As illustrated in FIG. 20, any one of the laser beam producingdevices of the present invention can be incorporated a body-wearablelaser scanning system, as well as a finger-mounted laser scanningsystem.

[0438] As illustrated in FIG. 21, any one of the laser beam producingdevices of the present invention can be incorporated a holographic laserscanning system.

[0439] As illustrated in FIG. 22, any one of the laser beam producingdevices of the present invention can be incorporated a CD-ROM discplayback system.

[0440] As illustrated in FIG. 23, any one of the laser beam producingdevices of the present invention can be incorporated a laser pointingdevice.

[0441] As illustrated in FIG. 24, any one of the laser beam producingdevices of the present invention can be incorporated a medical lasersculpturing system.

[0442] Any of the hand-supportable, body-wearable, or other scanningsystems described hereinabove may embody one or more of the followingfunctionalities: the spatially overlapping object detection and laserscan fields taught in U.S. Pat. No. 5,468,951; thelong-range/short-range modes of programmable scanning operation taughtin U.S. Pat. No. 5,340,971; the power-conserving system-controlarchitecture taught in U.S. Pat. No. 5,424,525; and the RF signaltransmission functionalities and acoustical acknowledgement signallingtaught in copending U.S. patent application Ser. No. 08/292,237, each ofwhich is commonly owned by Metrologic instruments, Inc. of Blackwood.

[0443] Modifications That Come To Mind

[0444] While each of the previous module designs has twoODOE's, it ispossible to design a module with three or more DOE's if desired orrequired by a particular application. One possible reason for desiringadditional DOEs might be a need for more beam shaping than canreasonably be provided by only two DOE's. While three or more DOEs wouldbe acceptable, one DOE would not be acceptable, due to the excessiveamount of dispersion produced by diffractive optics. This is not aproblem for multiple DOE's because they can be specifically designed tohave a net dispersion of zero when combined together.

[0445] The various embodiments of the laser beam producing system hereofhave been described in connection with linear (1-D) and 2-D code symbolscanning applications. It should be clear, however, that the apparatusand methods of the present invention are equally suited for use in otherapplications including, for example, scanning alphanumeric characters(e.g. textual information) in optical character recognition (OCR)applications.

[0446] Several modifications to the illustrative embodiments have beendescribed above. It is understood, however, that various othermodifications to the illustrative embodiment of the present inventionwill readily occur to persons with ordinary skill in the art. All suchmodifications and variations are deemed to be within the scope andspirit of the present invention as defined by the accompanying claims toInvention.

[0447] a laser beam source, such as a visible laser diode (VLD), forproducing a laser beam from its junction;

[0448] a collimating lens (L1) for collimating the laser beam as it istransmitted through collimating lens L1 and through the system in anS-incident manner;

[0449] a fixed spatial-frequency diffractive optical element (doe)denotable by D1;

[0450] a fixed spatial-frequency diffractive optical element (DOE)denotable by D2; and

[0451] a focusing lens (L2) disposed between DOE D1 and DOE D2 andadjustably translatable along its optical axis for focusing the outputlaser beam to some point in space.

73. The laser beam producing system of claim 72, wherein saidcollimating lens (L1) is realized by an optical element selected fromthe group consisting of a refractive lens, a HOE, a CGH, other type ofDOE, a grin lens, and one or more zone plate(s).
 74. The laser beamproducing system of claim 72, wherein each said DOE is realized by anoptical element selected from the group consisting of a HOE, acomputer-generated hologram (CGHs), a surface-relief hologram, and otherdiffractive optical element.
 75. The laser beam producing system ofclaim 72, wherein the total beam-shaping factor (M=M₁M₂) for the laserbeam modifying subsystem is less than unity (1), that is M1*M2<1, andthus the laser beam leaving the collimating lens (L1) is compressed inone dimension.
 76. The laser beam producing system of claim 72, whereineach of said DOEs is realized by an optical element selected from thegroup consisting of a HOE, a CGH, a surface-relief hologram, and otherdiffractive optical element.
 77. The laser beam producing system ofclaim 72, wherein said focusing lens (L2) is realized by an opticalelement selected from the group consisting of a refractive lens,holographic optical element (HOE), diffractive optical element (DOE),grin lens, and zone plate(s).
 84. A laser beam producing systemcomprises: a laser beam source, such as a visible laser diode (VLD), forproducing a laser beam from its junction; a collimating lens (L1) forcollimating the laser beam as it is transmitted through collimating lensL1 and through the system in a P-incident manner; a fixedspatial-frequency diffractive optical element (DOE) denotable by D1; afixed spatial-frequency diffractive optical element (DOE) denotable byD2; and a focusing lens (L2) disposed between DOE D1 and DOE D2 andadjustably translatable along its optical axis during the alignmentstage of the system assembly process for focusing the output laser beamto some point in space.
 85. The laser beam producing system of claim 84,wherein said collimating lens (L1) is realized by an optical elementselected from the group consisting of a refractive lens, a HOE, a CGH,other type of DOE, a grin lens, and one or more zone plate(s).
 86. Thelaser beam producing system of claim 84, wherein each said DOE isrealized by an optical element selected from the group consisting of aHOE, a computer-generated hologram (CGHs), a surface-relief hologram,and other diffractive optical element.
 87. The laser beam producingsystem of claim 84, wherein each of said DOEs is realized by an opticalelement selected from the group consisting of a HOE, a CGH, asurface-relief hologram, and other diffractive optical element.
 88. Thelaser beam producing system of claim 84, wherein the total beam-shapingfactor (M=M₁M₂) for the laser beam modifying subsystem is greater thanunity (1), that is M1*M2>1, and thus the laser beam leaving thecollimating lens (L1) is expanded in one dimension.
 89. The laser beamproducing system of claim 84, wherein said focusing lens (L2) isrealized by an optical element selected from the group consisting of arefractive lens, holographic optical element (HOE), diffractive opticalelement (DOE), grin lens, and zone plate(s) or the like.